DECEMBER 1975 $1.50 





nAfl, 



the small systems journal 



What is a Character? 

Assembling an Altair 

Logic Testers Galore 



A New 6800 Kit 




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Introducing 

. . .the world's 
lowest cost 
computer system 





All kits are delivered with a complete instruction manual and packaged for easy visual identifica- 
tion of parts to aid you in assembly. 



JOLT® is the new, fully-tested microcomputer with the exclusive on-board DEMON® debug 
monitor. You can build it, plug it in and talk to it in three hours or less ... for a price of just $249! 

The basic JOLT® card includes an 8-bit 
MOS Technology Model 6502 CPU, which 
requires no clock, can directly address 
65k of memory, has two index registers, 
58 instructions with 11 addressing 
modes, two interrupts and includes both 
single step and address halt capability. 
And that's only a part of it. 

JOLT's s CPU card is available 
IMMEDIATELY* in either kit form or as- 
sembled ($249 for the kit in single quantity 
and $348 assembled). Either way, the 
JOLT® CPU is completely tested prior to 
delivery. It comes complete with a termi- 
nal interface (TTY or EIA) and a unique 
software DEbugger/MONitor called 
DEMON®, for which full documentation is 
provided. It is very easy to program, and 
any JOLT® delivery includes an easy-to- 
follow assembly instruction manual, show- 
ing you exactly how to put everything 
together . . . correctly. Complete assem- 
bly should take you no more than three 
hours if you choose the CPU in kit form. 
Besides the JOLT® CPU — the 6502 from 
MOS Technology —the basic JOLT*' 
card has a fully static memory accom- 
modating 512 bytes of the user RAM. The 
JOLT® CPU memory also has 64 bytes of 
interrupt vector RAM. ROM Program 
memory on the basic card consists of 1k 
bytes of monitor/debugger with an au- 
tomatic Power-On bootstrap program 
— so you can start talking to JOLT® and it 
to you as soon as you plug it in to your 
terminal. On-board Input/Output devices 
on the JOLT® CPU card include TTY 20 
milliamp current loop and an EIA inter- 
face, both full duplex. The card has high 
speed reader interface lines and 16 fully 
programmable user I/O lines with lull TTL 
drive. 

Nobody, but nobody, except MAI can 
offer you an on-board debugger/monitor 
like DEMON®. It's fully documented, 
too. 

The exclusive DEMON® Debug Monitor 
really makes JOLT® one of the most out- 
standing computer systems offered at any 
time, at any price. Even without DEMON® 
and its superior software features, JOLT® 
is the lowest cost computer system in exis- 
tence. And DEMON- is a bonus you'll 
have to use to believe. First, it self-adapts 



to any terminal speed from 10-30 CPS. 
With it. you can display and alter your CPU 
register and memory locations, plus you 
can read, write and punch Hex formatted 
data . . . with Write/Punch BNPF format 
data for PROM programmers. It has unli- 
mited breakpoint capability along with 
separate non-maskable interrupt entry 
and identification. External device inter- 
rupts can be directed to any location you 
choose, or they can be defaulted to 
DEMON® recognition. DEMON® also 
gives you (1) a completely protected ROM 
resident debug/monitor; (2) the capability 
to begin execution at any location in mem- 
ory; (3) the capability to bypass DEMON® 
entirely to permit full control by you over 
your system; (4) a high-speed 8-bit parallel 
input option; and (5) it includes user calla- 
ble DEMON® I/O subroutines. MOST IM- 
PORTANT, DEMON™ IS INCLUDED AS 
STANDARD WITH ANY JOLT® CPU KIT 
OR ASSEMBLED BOARD! 

Obviously, the JOLT® basic card is a 
computer in and of itself. But you can add 
significantly to its capacity and versatil- 
ity by adding 4k RAM JOLT® memories 
— in one card or a whole bunch. A RAM 
card kit is only $265 ($320 assembled). 

NOW. 4096 Bit RAM 4K BYTE 

The JOLT® memory card is a fully static 

4,096-bit Random Access Memory (RAM) 
with 1 microsecond access time and on- 
board decoding. It is also available now.* 



And the quantity of one price is what you 
might expect to pay in quantities of 
100 .. . very inexpensive! 

There's also a JOLT® 1/0 card for you, 
our Peripheral Interface Adapter. You 
can't beat the price — single kit 96 
bucks — or the function. 




Pictured above is the assembled JOLV" CPU 
card with DEMON"", just plug it in and you're 
ready to go. 

The JOLT® PIA (Peripheral Interface 
Adapter) I/O card includes two PIA LSI 
chips, 32 input/output lines, two interrupt 
lines, on-board decoding and standard 
TTL drive. It is also fully programmable 
and available IMMEDIATELY* in either kit 
or assembled form ... at a very attractive 
single unit price ($140 assembled). 

Considering the function and capacity of 
the JOLT® Power Supply Card, you 
probably think the quantity of one price 
— $145 — is a misprint. It isn't. 

The JOLT- family also includes a power 
supply card, which operates at any of 



three voltages — +5, +12 and -10. The 
power supply supports the basic JOLT® 
CPU card, plus 4,096 bytes of RAM and 
I/O. The only two words for the price are 
"dirt cheap." It is available for delivery 
immediately with a single unit kit price of 
$145 ($190 assembled). 




The assembled power supply card shown 
above powers the JOLT& CPU, 110, and RAM 
Memory cards. 

You can also choose a blank JOLT® uni- 
versal card. Or several. 



The JOLT® Universal card is completely 
nude. It's a blank you can use any way 
you wish, for control panels, T.V. inter- 
faces, keyboards, LED's, or any other in- 
terface logic, because the card's holes 
are drilled to accept 14, 16, 24, or 40 pin 
sockets and has the same form factor as 
the other JOLT® cards. The single unit 
price is just $25. 

If you think you need extra cables, wires 
and the like, choose a Super Value 
JOLT® Accessory Bag. A $55 Value for 
just $40. 

The JOLT® Accessory Bag includes 25 
separate parts, enough hardware to con- 
nect one JOLT® card to another. Order an 
Accessory Bag for each additional JOLT® 
card. The Bag contains such necessary 
items as flat cable, connectors, cord 
spacers, hardware, wire, etc. 



THE JOLT PLAIN ENGLISH WARRANTY 

All components in the JOLT® family are 
new and fully tested prior to shipment. Kil 
components are fully warranted during the 
first 60 days of ownership. Assembled 
parts are fully warranted during the first 6 
months of ownership. If your properly as- 
sembled kit does not work, just ship your 
order back to Microcomputer Associates 
Inc. and we'll repair, replace, or refund 
your money. 



20% BONUS 

NOW! Special ONE TIME BONUS DISCOUNT. 
Order one CPU before November 10, 1975 and 

deduct 20% off of all additional cards and ac- 
cessories. (Note: Discount does not apply to 
CPU cards, assembled or unassembled.) 



We told you JOLT® was the world's lowest priced computer system. These prices prove it. 



JOLT KITS 

(ALL PAYMENTS MUST BE IN U.S. DOLLARS) 

QUANTITY PRICING 

1-4 5-19 20-49 50-99 100 up 



JOLT® CPU 
JOLT® RAM 
JOLT® I/O 
JOLT® POWER 

SUPPLY 
JOLT® UNIVERSAL 

CARD 
JOLT® ACCESSORY 

BAG 



$249 $235 $230 $225 



265 
96 



145 



25 



40 



255 

90 

135 
20 
36 



250 
88 

130 

18 

34 



245 
82 

128 

16 
32 



$215 

235 

75 



115 
14 
30 



ALL JOLT® KITS ARE DELIVERED COMPLETE WITH A DETAILED 
AND ILLUSTRATED ASSEMBLY MANUAL 

* Order will be shipped within 15 days. 



JOLT® ASSEMBLED PRICES 

(ALL PAYMENTS MUST BE IN U.S. DOLLARS) 

QUANTITY PRICING 

1-4 5-19 20-49 50-99 100 uc 



JOLT® CPU 
JOLT® RAM 
JOLT® I/O 
JOLT® POWER 
SUPPLY 



$348 $325 $320 $315 $305 

320 305 300 295 280 

140 125 120 115 105 



190 



175 



170 



165 



150 



THE NEW JOLT® FROM MAI IS AVAILABLE ONLY ON A DIRECT BASIS. 
USE THIS COUPON TODAY TO ORDER FROM 



Microcomputer Associates Inc. 

111 Main St., Department G 
Los Altos, Calif. 94022 
Phone (415) 941-1977 




3 1975 Pehaco Corporation 



I 



This coupon will bring you a JOLT®! Complete 



and return it. 



Here is my check, money order or credit card payment for the 
following JOLT® products. If a U.S. or Canadian order, please add 
$4.86 for shipping, handling and insurance. (Orders to ail other 
countries are priced F.O.B. Los Altos and will be shipped FREIGHT 
COLLECT.) 



Send me immediately: 

QUANTITY 



PRODUCT 



PRICE 



. JOLT® CPU KIT 

. JOLT®RAM MEMORY KIT 

. JOLT® I/O KIT 

. JOLT® POWER SUPPLY KIT 

. JOLT® UNIVERSAL CARD 

_ JOLT® ACCESSORY BAG 

_ JOLT® CPU ASSEMBLED 

_ JOLT® RAM MEMORY ASSEMBLED 

.JOLT® I/O ASSEMBLED 

_ JOLT® POWER SUPPLY ASSEMBLED 

TOTAL 



+ U.S./CANADA SHIPPING/HANDLING/INSURANCE 4.86 

NOTE: CALIFORNIA RESIDENTS, +6% SALES TAX 

TOTAL REMITTANCE (U.S. DOLLARS ONLY) $ 



I 



MAIL 
YOUR 
ORDER 
TO: 



Pehaco Corporation, JOLT® Sales Agents 
Microcomputer Associates Inc. Dept. G 

111 Main St., Los Altos, Ca 94022 

All orders subject to the prior approval of the manufacturer 




20% 
BONUS 



NOW! Special ONE TIME BONUS DISCOUNT. 
Order one CPU before November 10, 1975 and 
deduct 20% off of all additional cards and ac- 
cessories. (Note: Discount does not apply to 
CPU cards, assembled or unassembled.) 



20% 
BONUS 



PLEASE CHARGE THE TOTAL TO MY CREDIT CARD: 
BANKAMERICARD # 

MASTER CHARGE # 



My credit card expires on 
SIGNATURE 



(include 4-digit #) 



All credit card orders must be signed!) 

I UNDERSTAND THAT ALL U.S. ORDERS WILL BE SHIPPED VIA U.P.S. AND ALL 
INTERNATIONAL ORDERS WILL BE SHIPPED BY AIR. SEND MY ORDER TO: 



ORGANIZATION 
CITY 



STATE _ 
PHONE 



ZIP 



(Include Area Code) 

Make your check payable to: Microcomputer Associates Inc. 

International Orders: Payment should be cabled to Account 

#0041 7-06355 Bank of America, 215 So. Murphy 
Avenue, Sunnyvale, California, USA, 94086 



i 



|w non-shorting ac 








Part 




Model 


Row Dim. 


Number 


Price 


TC-8 


.3 IN. 


923695 


$7.35 


TC-14 


.3 IN. 


923698 


4.50 


TC-16 


3IN. 


923700 


4.75 


TC-16 LSI 


.5/. 6 IN. 


923702 


8.95 


TC-18 


.3 IN. 


923703 


10.00 


TC-20 


.3 IN. 


923704 


11.55 


TC-22 


.4 IN. 


923705 


11.55 


TC-24 


.5/. 6 IN. 


923714 


13.85 


TC-28 


.5/. 6 IN. 


923718 


15.25 


TC-36 


.5/. 6 IN. 


923720 


19.95 


TC-40 


.5/. 6 IN. 


923722 


21.00 



fast, 
access 
to all leads on dual-in-line 
IC packages 



No more shorting across 
DIP leads... just quickly 
clip on an IC TEST CLIP 
to bring DIP leads out for 
safe attachment of scope 
probes and other leads. 
Ideal for signal input, trac- 
ing, troubleshooting, etc. 
Patented precision, "con- 
tact comb" design guar- 
antees no shorting be- 
tween DIP leads. Probes 
can hang "no-hands" free 
on Test Clip terminals in 
card racks (unique — see 
photo). Engineered Me- 
chanical clamping plus 
gold-plated phosphor 
bronze terminals provide 
superior electrical con- 
tact. Also unequaled as a 
DIP removal tool. 



We honor M.C. and B.A.C. charges. 

Add sales tax on OH and CA orders. 

(F.O.B. Painesville on company P.O.'s.) 

Dealer inquiries invited 



Add — »- 
fees from 
this chart. 



SHIPPING/HANDLING 



Up to $10.00 $1.00 

$10.01 10 $25.00 1.50 
25.01 to 50.00 2.00 




All products guaranteed to meet or exceed published specifications 

AP PRODUCTS INCORPORATED 

Box 110-G • Painesville, OH 44077 • 216/354-2101 







fastest, most reliable 

method known. ..to build, test 

and modify experimental circuits 



8-bus distribution system 
plus universal .1" by .1" matrix 
of solderless, plug-in tie points 

all in one integral device. 

Accepts all DIP'S and discretes 
with leads up to .032" dia. 

Interconnect with any solid wire 
up to No. 20A.W.G. 

ORDER BY PART NUMBER 

. 923252 Inickel-siLver teiminils) $17.00 

923748 Igold-platsd terminals) $18.90 



High-performance A P Super- 
Strip component matrices consist 
of 128 terminals of 5 tie points 
each. The 8 buses of 5 connect- 
ed 5-tie-point terminals are for 
voltage, ground, reset and clock 
lines, shift command, etc. New, 
non-shorting, instant-mount 
backing and quick-removal 
screws are supplied... use several 
Super-Strips to create large-scale 
breadboards on panels up to 
1/8" thick. 



We honor M.C. and B.A.C. charges. 

Add sales tax on OH and CA orders. 

(F.O.B. Painesville on company P.O.'s.) 

Dealer inquiries invited 



Add — ■> 
fees from 
this chart. 



SHIPPING/HANDLING 



Up to $10.00 $1.00 

$10.01 to $25.00 1.50 
25.01 to 50.00 2.00 




All products guaranteed to meet or exceed published specifications 

AP PRODUCTS INCORPORATED 

Box 110-G* Painesville, OH 44077* 216/354-2101 



itiv e I 



rfo^er's 



ma if pistr'^ps 



solderless 

plug-in 
tie-points 




Super-Versatile™ 

building blocks for experimental circuits 



Universal .10" matrices of 
solderless, plug-in tie points 

For all DIP's and discretes 
with leads to .032" dia. 



Interconnect with any solid 
wire up to No. 20 A.W.G. 

Nickel-silver terminals 



ORDER BY PART NUMBER 
923277 distribution strip . . .$2.50 
923261 terminal strip $12.50 



Create custom breadboards in minutes 
with these new instant-mount strips. 
DISTRIBUTION STRIP (top) contains 
2 continuous buses of 12 connected 4- 
tie-point terminals. Size: 6.5" by .35". 
TERMINAL STRIP contains 128 5-tie- 
point terminals, holds up to nine 14-pin 
DIP'S. Size: 6.5" by 1.36". Integral, 
non-shorting, instant-mounting back- 
ing permits quick build-up of special 
breadboards using any mix of strips. 

Other models available. 



SHIPPING/HANDLING 



We honor M.C. and B.A.C. charges. Add( 

Add sales tax on OH and CA orders. f PP q'f n m Uptosio.oo st.oo 

(F.O.B. Painesville on company P.O.'s.) ,hj s cn °rt S' 001 ,oS250 ° ' - 60 
Dealer inquiries invited 



25.01 to 50.00 



2.00 



.70 
.80 
.90 




All products guaranteed to meet or exceed published specifications 

AP PRODUCTS INCORPORATED 

Box 110-G* Painesville, OH 44077 • 216/354-2101 






in • 

trV 11 




photo 
ACE 227 



On all models... 
simply plug in your 
>'" components and inter- 
connect with 22-ga. solid 
wire. All models accept all 
DIP'S, T0-5's and discretes 
with leads up to .032" diameter. 
Multiple buses can easily be linked for power and ground distribution, 
reset and clock lines, shift command, etc. Bases: gold-anodized alumi- 
num. Terminals: non-corrosive nickel-silver. Four rubber feet included. 



obsoletes """"• 

ordinary 

breadboards 



Order 


ACE 


Tie 


DIP 


No. 


No. 


Board Size 


Price 


No. 


Model No. 


Points 


Capacity 


Buses 


Posts 


(inches) 


Each 


923333 


200-K {kit) 


72B 


8(16's) 


2 


2 


4-9/16x5-9/16 


$18.95 


923332 


200 [assent.) 


872 


BUS'S) 


8 


2 


4-9/16x5-9/16 


28.95 


923334 


201-K (kit) 


1032 


12(14's) 


2 


2 


4-9/16x7 


24.95 


923331 


212 (assem.) 


1224 


12 114-s) 


8 


2 


4-9/16 X 7 


34.95 


923326 


218 (Bssem.) 


1760 


18(14's) 


10 


2 


6-1/2x7-1/8 


46.95 


923325 


227 (assem.) 


2712 


27 114's) 


28 


4 


8x9-1/4 


59.95 


923324 


236 (assem.) 


3648 


36(14's) 


36 


4 


10-1/4x9-1/4 


79.95 



We honor M.C. and B.A.C. charges. 

Add sales tax on OH and CA orders. 

(F.O.B. Painesville on company P.O.'s,) 

Dealer inquiries invited 



Add — ». 
fees from 
this chart. 



SHIPPING/HANDLING 



UptoSlO.OO $1.00 

$10.01to $25.00 1.50 
25.01 to 50.00 2.00 




All products guaranteed to meet or exceed published specifications 

AP PRODUCTS INCORPORATED 

Box 110-G* Painesville. OH 44077 • 216/354-2101 



In the Queue 



Foreground 



POWERLESS IC TEST CLIP 26 

Test Equipment — Baker — Errico 
LIFE Line 3 48 

Applications — He liners 
BUILD A 6800 SYSTEM WITH THIS KIT 72 

Hardware Review — Kay 
CAN YOUR COMPUTER TELL TIME? 82 

Applications — Hogenson 
PHOTOGRAPHIC NOTES ON PROTOTYPE CONSTRUCTION . . .94 

Hardware — Helmers 



Background 



THE SOFTWARE VACUUM 12 

Opinion — Ryland 
LOGIC PROBES - HARDWARE BUG CHASERS 20 

Tools — Burr 
WHAT IS A CHARACTER? 30 

Fundamentals — Peshka 
FLIP FLOPS EXPOSED 58 

Hardware — Browning 
READ ONLY MEMORY TECHNOLOGY 64 

Hardware — Lancaster 
THE HP-65: WORLD'S SMALLEST COMPUTER 70 

Systems — Nelson 
ASSEMBLING AN ALTAIR 8800 78 

Hardware — Zarrella 



Nucleus 



BYTE magazine is published 
monthly by Green Publishing, 
Inc., Peterborough, New 
Hampshire 03458. Subscription 
rates are $12 for one year 
worldwide. Two years, $22. Three 
years, $30. Second class postage 
application pending at 
Peterborough, New Hampshire 
03458 and at additional mailing 
offices. Phone: 603-924-3873. 
Entire contents copyright 1975 
by Green Publishing, Inc., 
Peterborough NH 03458. Address 
editorial correspondence to 
Editor, BYTE, Peterborough NH 
03458. 



In This BYTE 4 

What This Country Needs 5 

BOMB 9 

Diagnostics 10 

BYTE's Bits 17, 88, 98 

Word Hunt 18 

Clubs, Newsletters 100 

Letters 102 

Book Reviews 108 

The BYTE Questionnaire 112 

Reader's Service 112 



EITI #4 



DECEMBER 1975 




p. 20 




p. 26 




p. 72 




p. 78 




p. 94 




In This BITE 



In the Christmas BYTE you'll find the following morsels: 



To quote an ancient philospher, "nature abhors a 
vacuum." Chris Ryland's Opinion: The Software Vacuum 
describes a void in the personal use computer marketplace. 
Will nature in the form of profit motive come in and fill the 
software vacuum? Only time will tell . . . 

Strange things sometimes occur in the electronic pathways 
of a computer. Putting on your detective hat may occasionally 
be required — in which case Alex. F. Burr's review Logic 
Probes — Hardware Bug Chasers will give you valuable 
information on several commercial products which can help 
debug your designs. 

On the same theme but in the foreground this time, Robert 
Baker and John Errico have provided an article on a fairly 
sophisticated Powerless IC Test Clip which you can construct 
for $20 or so in parts. For the do-it-yourselfer, this design 
results in 16 little binary voltmeters which can be clamped 
onto an integrated circuit to examine the logic levels at each 
pin. 

What is a Character? You can find out by reading Manfred 
Peshka's tutorial on some of the basic concepts of program- 
ming and information systems work. Old hands at the 
programming arts will find this to be an interesting review, and 
readers new to programming will find it necessary background 
material. 

After an interruption, the LIFE Line series continues this 
month with the third installment. In LIFE Line 3 you'll find 
the beginning of information on the interactive commands 
which are decoded by the program. 

The Flip Flop is an important element in designs used with 
computer chips and peripherals. William E. Browning has 
provided this article to introduce the less experienced readers 
to this fundamental building block. 



Read Only Memory Technology can be used in situations 
ranging from clever logic and interface design to storage of 
systems programs in a computer. In his article on the subject 
in this issue, Don Lancaster gives some background informa- 
tion about ROM applications and several suggestions con- 
cerning their use as design elements. 

What is The World's Smallest Computer System? Well, at 
this time it looks like the HP-65 pocket-size programmable 
calculator might qualify for the title. Find out why by turning 
to Richard Nelson's article on the subject. 

The last BYTE featured a comparison of the Motorola 6800 
CPU chip with a new contender from MOS Technology. In this 
issue, Gary Kay of Southwest Technical Products Corporation 
presents some information on the Motorola 6800 package his 
firm is supplying. What SWTPC has done is to take the 
standard parts, combine them with an attractive case, power 
supply and PC boards — and put the result into a package as a 
kit for readers to build. 

What is it like to build an Altair computer kit? In his First 
Person Report: Assembling an Altair, John Zarrella describes 
his experience with the MITS product, from his decision to 
purchase, through assembly and hardware debugging. 

Computers are fundamentally synchronous machines — 
they beat to the tune of a periodic clock. With program timing 
loops, a computer can be made to count the beats of its clock. 
You can find out how to do this by reading Jim Hogenson's 
article Can Your Computer Tell Time? 

When assembling complicated logic systems, one of the best 
methods for new and experimental work is use of solderless 
wire wrap interconnection. Some pointers on prototype 
assembly are found in Photographic Notes on Prototype 
Construction. 

And on the cover, artist Robert Tinney illustrates the 
impact of these new toys upon traditional relationships. 



What This Country Needs 
Is a Good 8- Bit 
High Level Language 



Have you ever tried to talk 
to a person who speaks a 
language other than your 
own? You know that the 
person must think as a 
rational, sentient being or 
you wouldn't make the 
attempt to communicate. As 
a human being your 
conversational partner's basic 
thought patterns are of 
necessity similar. Yet you 
can't understand him and he 
can't understand you. There 
are ways around this 
problem, given a sincere 
interest in communications 
by both parties. 

An analogous problem 
exists in the field of personal 
computing as it is practiced 
by the readers of BYTE. If 
you translate the words 
referencing human beings 
into words referencing 
computers and reread the 
preceding paragraph, the 
result will be a corresponding 
statement about the 
computer communication 
problem: In the home brew 
computer world, there are a 
number of different 
computer architectures, all 
speaking different machine 
languages. There are even 
dialects of machine languages 
since each home brew 
designer or manufacturer 



Editorial 

by 

Carl Heimers 



makes specific choices about 
address space allocations and 
input/output port 
assignments used with the 
standard computer chip 
designs. Yet all of these 
machines are potentially 
programmable to do similar 
functions. 

Like two human beings 
facing each other but 
speaking different languages, 
computers can talk to each 
other on compatible channels. 
But making sense — that is to 
say, executing the same 
programs — is another matter. 
It is possible to connect an 
Altair up to a Scelbi 8H 
product using an RS-232 
interface. The link can be 
made and every bit of every 
byte sent (for example) from 
the Altair will be received and 
digested by the Scelbi. But 
unless the machines have 
common referents and means 
of translation, the 
information sent will be no 
better than "noise" — just as 
a foreign language perceived 
by a person conveys no more 
meaning than an arbitrary 
sound until the language is 
learned. Having a working 
communications channel does 
not guarantee that the 
communications sent will 
mean anything. 



Levels of Intelligence 

Given two or more 
different computers and 
compatible electrical 
interfaces between them, the 
simplest and easiest form of 
common understanding is at 
the level of raw data to be 
processed by the different 
computers. A binary number 
is a binary num ber 
independent of the machine 
for which it was generated. 
The fact that the bit string 
11000111 means "load 
accumulator from memory" 
in the machine language of an 
8008 and means "You fool — 
that's an unimplemented op 
code" for the Motorola 6800 
is an accident of hardware 
design at two different 
companies. In either case, as 
data, the binary number 
11000111 means an integer 
value of 199. Similarly, an 
ASCII character is an ASCII 
character independent of the 
place and time of its creation. 
Given the decision to use 
ASCII for communications — 
or binary numbers, for that 
matter — both parties to the 
communication can talk 
characters or numbers. These 
simple data formats provide 
an easily implemented link 
between computers which 



BITE 

staff 



EDITOR 

Carl T. Heimers Jr. 
PUBLISHER 
Wayne Green 
MANAGING EDITOR 
Judith Havey 
ASSOCIATE EDITORS 
Dan Fylstra 
Chris Ryland 

CONTRIBUTING EDITORS 
Hal Chamberlin 
Don Lancaster 

ASSISTANT EDITOR 

Beth Alpaugh 

PRODUCTION MANAGER 

Lynn Panciera-Fraser 

ART DEPARTMENT 

Nancy Estle 

Neal Kandel 

Peri Mahoney 

Bob Sawyer 

PRINTING 

Biff Mahoney 

PHOTOGRAPHY 

Bill Heydolph 

Ed Crabtree 

TYPESETTING 

Barbara Latti 

Marge McCarthy 

ADVERTISING 

Bill Edwards 

Nancy Cluff 

CIRCULATION 

Pat Geilenberg 

Dorothy Gibson 

Pearl Lahey 

Charlene Lawler 

Judy Waterman 

INVENTORY CONTROL 

Marshall Raymond 

Kim Johansson 

DRAFTING 

Bill Morello 

COMPTROLLER 

Knud E. M. Keller 



JF?\U- GOWOUT CLCCJttONfcS^B 



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^0 «fl c/QYQUS HOLIDAY s ^ 

AND HOPE THAT 76 WILL BE YQUR 

-B BEST YEAR EVER S* 




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segment and driver 
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We include all parts you need 
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cluding the PC board, trans- 
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supply the case and hardware. 




"Electronic Projects 
for Musicians" 

BY CRAIG ANDERTON $6,95 sh + Pg 



they 
^ii^j^ijiC also 

$M 5 v^ egrcat ^ 



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AN IDEAL BOOK FOR PEOPLE INTO 
MUSICAL ELECTRONICS... contains 4 chapters for be- 
ginners on practical electronics, so that even 
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book then describes 19 projects suitable for any 
level of experience, such as a ring modulator, 
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fuzz, compressor, 5 12 more. Also has sections on 
troubleshooting, finding more informa- 
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Walsh, and a recording that 
demonstrates the sound of 
the proj ects . 



for any other electronics enthusiast you 
know. Scope our FLYER for more toys ! 



wm HOARD §PI«l ©FFi^ 

By special arrangement with a software house (meaning we pay them royalties), we've got 4K by 8 EROM boards 
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BOX 2355, OAKLAND AIRPORT, CA 94614 



does not require a large 
amount of software 
intelligence on the part of 
receiving and sending 
computers. It does not matter 
whether such a link is in the 
form of tape cassettes sent in 
the mail or a direct RS-232 
connection when all the 
neighborhood hackers get 
together for a multiprocessor 
powwow and computerized 
crap game. ASCII and binary 
numbers can be shuffled back 
and forth with the assurance 
that, at this data level of 
coding, the information will 
be understood by both 
parties. 

The communication 
represented by binary 
numbers or ASCII encoded 
data is not at all what might 
be called true understanding 
between the two computers 
involved. Sending data is a 
first step, but it is by no 
means the ultimate. The 
significance of the 
communication at this level 
must be determined by the 
human beings who 
manipulate the data being 
sent. There is no direct way 
of affecting the 
understanding — the 
programming — of the 
computer which is dutifully 
receiving the ASCII or binary 
data in this simple fashion. 

Simple transmission of 
data across a parallel-serial- 
parallel or parallel-parallel 
interface enables the users of 
the computers to talk to one 
another, but the computers 
which carry out the exchange 
"couldn't care less." The 
computer in this type of an 
exchange is simply serving as 
a "dumb" transmission 
channel. 



YOU FOOL - THAT'S 
AN UNIMPLEMENTED 
OPCODE! 




BASIC is an adequate 
language — but it has its 
drawbacks. 



Borrowing again from the 
analogy to human beings, this 
data level communication 
between computers might be 
compared to the non-verbal 
emotional forms of 
interpersonal exchange. 
Common languages and 
verbal understanding are not 
required for humans to 
exchange emotional states, 
using music, facial gestures 
and other body motions 
which are inherent in the 
nature of the beast. But to 
exchange knowledge and 
practical data humans must 
speak a common language; it 
is not an accident that verbal 
activity and the tools of 
language are so much a part 
of the dominant species on 
this planet. If merely sending 
data represents a low level of 
communications intelligence 
between computers, what 
does it mean to transmit a 
higher level of intelligence? 

Program Level Intelligence 

To transmit data between 
computers is the first step 
toward a higher level of 
communications among 
diverse types of computers. 
Every computer on the 
market can handle 7-bit 
ASCII and other forms of 
information encoded into 
8-bit bytes. (Of course, it 
may be easier to program 
ASCII data manipulations on 



some machines than on 
others.) Having a computer 
which can easily be 
programmed (possibly with 
no human intervention) as a 
result of an ASCII exchange 
with a computer of a 
different internal architecture 
is the essence of this next 
level of intelligence in 
intercomputer communica- 
tions. In such program level 
exchanges the computers are 
speaking to each other in the 
form of abstract program 
representations which can be 
automatically translated into 
specific machine language 
representations for execution. 
In the previous analogy, 
this is like human beings 
exchanging information and 
thought in a commonly 
understood language — for 
example, English. Each 
person who understands the 
language has incorporated 
within his mind a 
"translator" which creates an 
internal understanding based 
upon what was heard. The 
result of this translation — 
which must be consciously 
performed — is an 
understanding of the message 
which can be used as a basis 
for further thoughts. 
Emotional data is a much 
more directly perceived input 
(although it may of course be 
colored by thoughts). But 
verbal inputs require 



cogitation and analysis before 
they can be used and 
integrated. 

The Goal: Exchange of 
Programs 

The goal of program level 
interchange between 
computers is thus the ability 
to communicate 
understandable and 
potentially executable 
programs between computers 
of different design. When this 
goal is achieved it will be 
possible for a reader in one 
corner of the technological 
world — for instance an 8080 
user — to develop a neat little 
utility program which can be 
sent to a friend in another 
corner of the technological 
world who has just completed 
a different processor such as a 
PACE machine. Since the 
program is recorded and 
communicated using the 
program level techniques, the 
recipient need only read the 
ASCII representation from 
the communications channel 
and process this data with a 
suitable "translator" in order 
to obtain a new executable 
program for a different 
machine design. 

This program level of 
exchange is a well known 
technique which has been 
developed very thoroughly 
over the past 1 5 years after 
computer science left its 
formative years of the 1 950's. 
It is the technique of high 
level languages and compilers. 
The language is the machine 
independent notation for the 
programs which are to be 
exchanged. The compiler is 
the computer program which 
carries out the translation. 
(Variations on this technique 
of course exist; for instance 
some languages like BASIC 
and FOCAL rarely have 
compilers, but typically use 
"interpreters" instead to 
compile, then execute 
statements one by one.) In 
the computer world at large, 
of course, there is no 
unanimity about choices of 
languages — and there no 



doubt will be considerable 
variation in program 
representation philosophies in 
this personal microcomputer 
field. Be that as it may, 
exchanges at the program 
level are needed and 
computer languages/com- 
pilers are the technique for 
accomplishing such exchanges 
with minimum machine 
dependence. 

So that's the story behind 
the need for a good 8-bit high 
order language. The home 
brew computing field is much 
more extensive than the 
confines of just one computer 
architecture, and the 
technological problem of 
passing 8-bit bytes all over 
the place is not at all 
impossible. The need is there, 
but can it be satisfied? 

What Exists Now? 

What currently exists in 
the way of high level 
languages for the field of 
home brew computers is 
limited. Currently available is 
only one language — BASIC 
— which to a certain extent 
satisfies the need for a good 
language. BASIC now exists 
for the MITS Altair, and will 
soon be offered by several 
other manufacturers. As such 
it is the only high level 
language which both exists 
and will (hopefully) run the 
same programs on any one of 
these small computer 
systems. As a high level 
language, BASIC is adequate 
but it has a few drawbacks: 

— Descriptive names of 
variables are impossible with 
single character identifiers. 

— Only a primitive 
GOSUB/RETURN facility 
exists for subroutine 
linkage, and parameter 
passing is not built into the 
language. 

— The language BASIC is 
intcrpretatively executed, 
which means that each 
statement is "compiled on 
the fly" and executed 
whenever it is encountered. 
(Pre-scanning of programs 
and reduction of the source 



text is sometimes done, 
however.) An interpreter is 
necessarily slower than an 
equivalent compiler's object 
code. 

— BASIC is missing the 
more advanced software 
tools such as the 
IF-THEN-ELSE construct, 
and statement grouping 
constructs, like the PL/1 
DO . . . END block. 

— Only line numbers may 
be used to label places in 
the program. 

Now don't make the mistake 
of concluding from this 
criticism that BASIC is 
useless. Far from it. Any high 
level language which works 
as well as BASIC is better 
than none at all in the 
majority of programming 
circumstances. This is because 
for most problems the minute 
details of execution arc 
unimportant, provided that 
certain functional building 
blocks of software (provided 
by the higher order language) 
are available to use. 

The BASIC language has 
been used as a tool for 
initially teaching computer 
programming concepts, and 
has done so from its 
inception in the early 1960's 
at Dartmouth. There are also 
innumerable tutorial books 
about BASIC, due to its 
widespread use in the 
educational field. It is 
certainly the case that in 
most implementations BASIC 
is a quick and conversational 
way to write simple programs 
at a terminal. The criticisms 
have to do with features in 
contemporary computer 
language technology which 
are not present in BASIC, but 
which are extremely useful 
when writing programs. 

An Alternative to BASIC 

Criticism without giving an 
alternative is an empty 
activity. The purpose of 
criticism is to find a way to a 
better approach. So what 
language exists, can be 
dreamed up, or adapted to 
the small systems context — 



and provides a better 
alternative to BASIC? At 
present there is one language 
which was expressly designed 
for systems programming and 
applications programming for 
microprocessors. This 
language is called PL/M, 
which is a registered 
trademark of the Intel 
Corporation. The origins of 
PL/M can be traced back to a 
book published in 1970 by 
three compiler specialists, W. 
M. McKeeman, J.J. Horning 
and D. B. Wortman called A 
Compiler Generator 
(Prentice-Hall, Englewood 
Cliffs NJ). 

XPL is a subset of the IBM 
language PL/1. The XPL 
subset is designed to 
eliminate many extraneous 
bells and whistles from PL/1, 
retaining only those features 
most needed for writing 
compiler programs: Simple 
character string and binary 
data, manipulations of such 



In most programming 
circumstances, any high 
level language is better 
than no high level 
language at all. 



data, and a block structured 
procedure oriented language. 
Another design criterion of 
XPL is that it had to be a 
simple language so that its 
compilers could easily 
generate efficient object 
programs without burning up 
incredible amounts of 
computer time. The authors 
of the language and the book 
describing it succeeded well, 
producing a powerful 
language design system which 
has been used in a number of 
large projects. 

Now, as it turns out, the 
features which are in XPL are 
in many respects the features 



BOMB: byte 



's Ongoing Monitor Box 



BYTE would like to know how readers evaluate the efforts of 
the authors whose blood, sweat, twisted typewriter keys, smoking 
ICs and esoteric software abstractions are reflected in these pages. 
BYTE will pay a $50 bonus to the author who receives the most 
points in this survey each month. The following rules apply: 

1. Articles you like most get 10 points, articles you like least get 
(or negative) points — with intermediate values according to 
your personal scale of preferences. 

2. Use the numbers to 10 for your ratings, integers only. 

3. Be honest. Can all the articles really be or 10? Try to give a 
preference scale with different values for each author. 

4. No ballot box stuffing: Only one entry per reader. 1 

FiJJ out your ratings, and return it as promptly as possible along 
with your reader service requests and survey answers. Do you like an 
author's approach to writing in BYTE? Let him know by giving him 
a crack at the bonus through your vote. 

Page LIKED 

No. Article LEAST BEST 

12 Ryland: Software Vacuum 01 23456789 10 

20 Burr: Logic Probes 01 23456789 10 

26 Baker-Errico: Test Clip 0123456789 10 

30 Peshka: Characters 01 23456789 10 

48 Helmers: LIFE Line 3 0123456789 10 

58 Browning: Flip Flops 0123456789 10 

64 Lancaster: ROM Technology 01 23456789 10 

70 Nelson: HP-65 0123456789 10 

72 Kay: Build a 6800 0123456789 10 

78 Zarrella: Altair 8800 01 23456789 10 

82 Hogenson: Tell Time 0123456789 10 

94 Helmers: Photo Notes 01 23456789 10 



PL/M is becoming an 
industry standard 
language: The 
computer language 
equivalent of a "black 
box" integrated circuit.. 
BYTE would like to see 
a PL/M compiler 
adapted to the home 
brew computer 
context. 



which are desirable for a 
programming language used 
with microcomputers for 
both applications and systems 
programming. XPL is not too 
far removed from assembly 
language and becomes very 
handy as a way to generate 
large programs without 
getting bogged down in 
details. This fact makes XPL 
a language of far more utility 
than a mere compiler writing 
tool. 

When the time came for 
Intel to commission a high 
order language for 
programming of their 
microcomputers, the XPL 
language and compiler had 



been proven in several years 
of practical use by several 
compiler writing 
organizations. Its practicality 
as a systems programming 
tool no doubt resulted in the 
use of XPL as a model for the 
new PL/M language. PL/M is 
effectively an adaptation of 
XPL to the context of a 
microcomputer with 8-bit 
data quanta and 16-bit 
addressing. The result is a 
language which looks very 
much like XPL — with a few 
keyword substitutions and 
additional features. This 
resemblance is sufficiently 
close that at least one version 
of PL/M has been 
implemented simply by 
modifying a working XPL 
compiler, although Intel's 
original was implemented in 
FORTRAN. 

PL/M as a language 
possesses many desirable 
attributes which are not 
found in BASIC. These 
attributes include the 
PL/1 -like statements and 
statement groups, long 
descriptive names for 
variables and labels, block 
structure, and subroutine 
linkages with parameters. As 



DIAGNOSTICS: Documentation of bugs in previous 
BYTEs. 



BYTE #2, p. 54, Fig. 3. 
An inverter (e.g., 1/6 7404, 
or 1/4 7400) should be 
inserted between the CE 
inputs of the 7489 circuits 



and the 7400 which drives 
them in the original drawing. 
Thanks to Martin E. Haling, 
Edison NJ and several other 
readers for pointing this out. 



Dan Clarke (105 Fir 
Court, Fredericton NB, 
Canada E3A 2E9) notes that 
the originate modem transmit 
frequency definitions (Fig. 14 
and text of "Serial Inter- 
face"), page 35, BYTE #1, 



are incorrect. Using the 
Motorola M6800 Micro- 
processor Applications 
Manual page 3-32 as a source 
of data, the following table 
should correct the matter: 



Mode 


Data 


Transmit Freq. 


Receive Freq 


Originate 


Mark 


1270 Hz 


2225 Hz 


Originate 


Space 


1070 Hz 


2025 Hz 


Answer 


Mark 


2225 Hz 


1270 Hz 


Answer 


Space 


2025 Hz 


1070 Hz 



a systems programming 
language for microcomputers, 
the PL/M language adopts 
some of the features of an 
absolute assembler — there 
are location counters for 
program code and data which 
can be set during a 
compilation. To top it all off, 
the PL/M language is a 
relatively simple one which 
can potentially be 
self-compiled upon a small 
(but not minimal) home brew 
system. 

At the time of this writing, 
PL/M is fast on its way to 
becoming an industry 
standard. It is definitely a 
language which has the 
potential for adaptation to 
the software requirements of 
the more advanced 
programmers in BYTE's 
readership — yet at the same 
time it is simple enough for 
the novice to understand. At 
the present time, however, 
only cross compilers — large 
programs running on big 
machines — are available for 
PL/M. There are PL/M 
versions currently in the 
works or producing code for 
the 8080, the 6800 and 
PACE microcomputers — but 
all are cross compilers. These 
cross compiler versions are 
widely used via time sharing 
networks by a variety of 
industrial and commercial 
users of microprocessors. This 
acceptance indicates that 
PL/M is a language which is 
likely to be around for some 
time. 

A Call For Compilers 

So PL/M is the tool which 
the industrial and commercial 
world uses for efficient code 
generation with a high level 
language for microprocessors. 
Will this technology be made 
available in the home brew 
computer markets? Yes. One 
reason for writing this 
editorial is to point out the 
existence of PL/M and direct 
a few BYTE readers to 
appropriate sources of 
information. In future issues, 
BYTE will be getting into 



Information Sources 

PL/M: 

8008 and 8080 PL/M 
Programming Manual, 
MCS-451 -0275-1 OK 

Intel Corporation 

3065 Bowers Ave., Santa 
Clara CA 95051 

This describes 8008/8080 
PL/M as originated by Intel. 

PL/M6800: 

PL/M 6800 Programmers 
Reference and PL/M 6800 
Language Specification 

Intermetrics, Inc. 

701 Concord Ave. 

Cambridge MA 02138 

These manuals describe 
the version of PL/M being 
marketed for the 6800 pro- 
cessor. 

As this issue goes to press, 
National Semiconductor has 
announced a version of PL/M 
called "PL/M+" for the PACE 
system. Further details will 
be provided by BYTE as they 
become available. 



more of the details of PL/M 
as a language. Until then, the 
accompanying list of 
information sources will have 
to suffice. 

A second reason for this 
editorial is to serve as a call 
for compilers. What is needed 
is a compiler for PL/M or a 
similar language which will 
run on a typical 16K (RAM) 
8-bit microcomputer using as 
many as three serial I/O 
devices for multiple passes 
through the data of a source 
program. Ultimately there 
should be one such 
self-compiler program for 
each of the major 
microcomputer chip 
architectures. The compilers 
should be written with 
system design flexibility in 
mind (in other words, 
modularity throughout and 
isolation of hardware- 
dependent portions to 
specific modules). Who will 
be the first person, club or 
firm to provide such a 
self-compiler? ■ 



10 



One -Card 
Computer. 




• real-time clock 

• 16 digital I/O lines 

• 4k RAM 



• 512 times 8 PROM 

• serial teletype interface 

• hardwired ROM monitor 
(console emulator) 



(Complete with usage, programming, and application manuals.) 

Still, our price goes down a lot easier. 

Now's your chance to bite into a complete computer system. We at Sphere have used the latest 
microprocessing technology along with some real innovations in mini-circuit design to develop the 
lowest-cost complete computer systems available. We've found that most people find our CPU 
module hard to believe. This CPU can monitor functions on a real-time basis, analyze, and quickly 
arrive at answers in a desired format. It's expandable; and SPHERE offers a complete line of the 
lowest-cost peripherals on the market today. 



KIT* ASM' ONE-CARD COMPUTER: Includes Motorola 6800 microprocessor, 4K RAM, 512 bytes EPROM, (containing a Program Development 

$350 $520 System), a REAL-TIME CLOCK, 16 LINES OF DIGITAL I/O, serial type interlace and hard wired ROM monitor. 

'This is the OEM 100-quantity price, extended to the hobbyist, for a limited time, in quantities of one. 



SPHERE CORPORATION 

Dept. 1212 
791 South 500 West* 
Dear SPHERE: Bountiful, Ulah 84010 

Yes! The facts I've read have convinced me! 

D Enclosed is a check for the exact amount. Please send my 
ONE-CARD COMPUTER, for 60 day delivery. 

□ Please rush me more details on your low-cost computer 
system and peripherals. (Specific questions, if any, are 
attached.) 

Print Name: 

Address: 

City and State: 

Zip Code 



Phone: 




SPHERE 

CORPORATION 



791 South 500 West Dept. 1212 
Bountiful, UtahB4010 



(801)292-8466 



11 



Opinion: 



The Software Vacuum 



... I'd like to browse 
through several 
software catalogs . . . 
picking out the best 
package for my needs. 



by 

Chris Ryland 
25 Follen St. 
Cambridge MA 02138 



There is a software 
vacuum. That fact has 
become increasingly clear in 
the past few months. 

Take a look at the 
situation. At the time this is 
written there's only one 
company (MITS) offering a 
proprietary software product 
(BASIC) aimed directly at the 
microcomputer hobbyists. 
It's true that the People's 
Computer Company (PCC), 
the MITS Altair User's 
Group, and a handful of 
other user groups offer access 
to growing libraries of 
applications programs. Some 
microsystem manufacturers 
also supply "bare bones" 
system software with their 
machines, but the user is 
lucky if these bones consist 
of as much as a rather bare 
monitor, editor and 
assembler. Such software is 
just as important to a serious 
hobbyist's system as the 
hardware. So when I say 
there is a software vacuum, I 
mean there is an absence of 
commercially developed and 
marketed larger scale 
software products. 

But why should this 
matter to me, as a hobbyist? 



What do I mean by 
larger-scale, and why should 
the hobbyist market be 
invaded by commercial 
software vendors? In answer, 
let me give a concrete 
example. Suppose I want to 
write a "desk calculator" 
program for my system. I'd 
like it to include all the 
scientific functions of a 
powerful calculator, such as 
sine, cosine, tangent, arcsine, 
the hyperbolic functions, etc. 
I would feel competent to 
design and write the user 
interface (e.g., keyboard 
input) sections of the 
calculator, but when it comes 
to even the floating-point 
arithmetic (let alone the 
scientific) functions, I'm 
totally lost. What do I do? 
Give up? Scour the different 
user groups software 
offerings, piecing together 
little routines from here and 
there? Take a course in 
applied numerical analysis 
and learn enough theory to 
do all the programming 
myself? No. Ideally, I'd 
browse through several 
software catalogs from 
commercial vendors, picking 
out the best math package for 
my needs. It would be 
relatively inexpensive, 
because of competition 
among the various vendors. 
And since the time I save by 



buying the package 
commercially is substantial, 
I'd consider it to be a 
larger -scale product 
(physically small though it 
may be). Finally, and most 
important, is the assurance of 
quality that I get — the 
programs that I buy should 
be backed up by a 
guarantee; if they don't 
work correctly, I can have the 
problem fixed by someone 
who's an expert at that sort 
of thing. In fact, any 
problems discovered by other 
customers of the supplier will 
be automatically corrected 
and reported to me. 

I'm not pointing out 
anything surprising, though. 
What is surprising is that this 
lack of software is no one's 
fault. Why? The reasons will 
become clear as we examine 
the basis and effects of the 
vacuum more carefully. 

The most obvious 
explanation for the software 
vacuum is the newness of our 
field. It's very easy to draw a 
parallel to the very early days 
of "real" computers, when 
every manufacturer was 
scrambling to produce 
hardware. The importance of 
software wasn't recognized, 
and it was simply left behind 
in the dust. Since then, 
however, software has 
become the major 



component, in cost, size, and 
complexity, of any large 
computer system, since 
nothing can be done without 
it. 

The parallel is completed 
by noting that, now, the big 
''scramble" in micro- 
computers is to get out the 
hardware. People do 
sometimes learn from history, 
though. Microsystem 
suppliers have realized that 
naked machines are close to 
useless, and many are offering 
at least the bare bones system 
software mentioned earlier. 
The problem here is that 
many of us want to use our 
home or business system for 
something (e.g., as a powerful 
desk calculator) and don't 
necessarily want to do all the 
programming ourselves. 

This situation is eased, for 
example, by the availability 
of a BASIC system from one 
major supplier. Unfortunate- 
ly, for the "from scratch" 
hobbyist, the difficulty still 
remains, since software like 
BASIC is much more 
expensive as a stand-alone 
product (and is usually out of 
the price range of most of 
us). Again, since the average 
hobbyist would be lost when 
faced with the task of 
constructing his own BASIC 
system, he's thereby 
automatically cut out of the 



12 



You 9 1 1 go nuts over 
our computers! 




*L*i* 



And the Sphere Computer System costs 
less than anyone else's terminal. 

Completely intelligent micro-systems . . . that's what we offer. Just look at the features, and the 
prices. No compromising, with no short cuts! Recently at WESCON, SPHERE also demonstrated its 
new, full-color and B/W graphics terminal — and we have other new products, to be just as 
revolutionary as the SPHERE 1 SYSTEM was when we released it last June. SPHERE 'R & D' will keep 
ahead of your demands, no matter the state of the art. Take one look at our catalogue, then call or 
write us today. 



KIT ASM 
S860 $1400* 



SPHERE 1: This system includes the Motorola WJ00 microprocessor, 
4K RAM, 1K EPROM (containing an EDITOR, ASSEMBLER, DEBUG- 
GER, COMMAND LANGUAGE, CASSETTE LOADER, DUMPER, 
UTILITIES), a REAL-TIME CLOCK, plus 512 character video interface, 
with full ASCII keyboard and numeric/cursor keypad, power supply, 
chassis, manuals, and associated parts. 

SPHERE 2: Includes all fealures of SPHERE 1, plus serial communica- 
tions, and audio cassette or MODEM interface. 



SPHERE 3: Inlcudes all the features of SPHERE 2, plus memory 
2250" totaling 20K which is sufficient to run full extended BASIC Language. 



KIT ASM 
$6100 $7995* 



SPHERE 4: Includes all of Ihe features of SPHERE 3, except the 
cassette has been replaced by an IBM-compatable Dual Floppy Disk 
System. This system includes a Disk-operating system and BASIC 
Language and a 65 LPM line printer. 

OTHER SPHERE PRODUCTS: Light pen option; full color and B/W 

video graphics system; low cost Dual Floppy Disk System; and full 
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*This ASSEMBLED SPHERE Syslem includes the complete chassis, and video monitor 
as pictured below. 



The Whole System: 





SPHERE 

CORPORATION 



791 South 500 Wesl Depl. 1211 
Bountiful, Utah 84010 



(801)292-8466 



13 



Suppose you could 
make working Xerox 
copies of CPU chips, 
how long would chip 
manufacturers be 
around? 



Hobbyists can help 
generate commercial 
interest in producing 
software. 



legacy of widely-available 
BASIC programs. 

Now why can't we throw 
the blame on the CPU chip 
manufacturers? Because, 
clearly, their proper market is 
the OEMs (Original 
Equipment Manufacturers), 
and thus their main concern 
regarding software is to 
provide their OEM customers 
with developmental systems 
of hard and software, leaving 
the hobbyist nearly 
completely, if not 
intentionally, out of the 
picture. 

What about the other 
potential suppliers of 
software? Look at the 
situation of a typical software 
house, or vendor. They must 
ask, "What kind of hobbyist 
market exists? How big is it, 
and how can it be reached? 
What kind of return on 
investment can be expected 
from a venture in this area?" 
These are tough questions for 
a company whose existence 
depends on successful 
marketing of software 
products, even though the 
answers might seem obvious 
to us. But keep in mind that 
the existence of BYTE is 
among the first indicators of 
a widespread hobbyist 
interest in computing, and 
we're only a few months old. 

Furthermore, there's the 
problem of proprietary 
programs, a problem hard to 
appreciate from the 
hobbyist's point of view. It 
stems from the softness of 
software: Hardware can only 
be physically in one place at 
one time, but software, 
because its copying cost is 
(relatively) so low, can 
virtually be in many places at 
once. For example, an 
institutional computer 
installation signs a 
proprietary contract when it 
buys a program product. 
Such contracts typically 
restrict use of the software to 
one computer system or 
customer site. This is one of 
the major reasons the 
institution is not likely to 



lend or sell such a product to 
other installations. But a 
hobbyist, even though he 
might sign a similar contract, 
is much more likely to help 
out a friend by swapping a 
program for others, or by 
lending a copy to someone 
else. And this is deadly 
poison for any sort of 
commercial market. To take a 
concrete, if absurd, 
illustration, suppose you 
could make working Xerox 
copies of CPU chips — how 
long would the chip 
manufacturers be around? 

Another simple fact of 
proprietary-program life is 
that such programs cost a lot 
to develop and market. 
Unless the market is large, 
this means high prices, which 
a big computer installation 
can usually justify, but which 
an individual just can't 
afford. It's true that there's a 
difference in scale between 
large and micro system 
software, but both, in their 
own spheres, are costly to 
commercially develop and 
maintain. So, the software 
vendors may simply not have 
been able, even if willing, to 
enter the microcomputer 
software market. 

Continuing with our 
search for potential software 
suppliers, we arrive at the 
grass roots level: The home 
experimenter who's 
developed a good product 
with long hours and minimal 
tools. Why can't he go it 
alone? Well, he's usually 
operating on a small budget 
and thus can't mount any 
sort of larger marketing, 
packaging, or shipping effort. 
True, you might say, but 
couldn't he sell his product 
locally, at a neighborhood 
level? Yes, he could, but then 
he's not reaching the majority 
of people who are interested 
in his product, namely, us. 
Besides, how can he 
commercially support any 
product on even a medium 
scale, when such support 
might involve, aside from all 
the developmental and 



promotional work and 
expense, handling dozens of 
trouble reports in a single 
week? He'd no longer be a 
hobbyist, but a full time 
one-man software house, and 
that puts him out of the grass 
roots class. 

So, with our search ended, 
and no culprit in sight, what 
can be done about the 
software vacuum? 

First of all, those of us in 
the personal computing field 
who have professional 
contacts can urge existing and 
potential software vendors to 
look hard at the hobbyist 
markets. When the number of 
potential users of a package is 
multiplied by the profit 
margins to be expected, such 
software vendors should be 
economically viable. 
Whenever there is a demand 
for a product, a free market 
will tend to fill that demand. 
It will be interesting to see 
what the market produces in 
system software for small 
computers. 

Second, hobbyists can 
help generate commercial 
interest in this vital area in 
several ways. One is to make 
the software vacuum a topic 
for discussion at local 
computer club meetings. 
Another is to organize 
software trading posts in the 
newsletters which are very 
much a part of the hobby. 
Still another is to write 
manufacturers urging 
advanced software products 
to match the extremely high 
level of today's hardware 
technology. If you feel 
eloquent, write a letter to the 
editor of BYTE on the 
subject. 

The first step in filling a 
need is identifying that the 
need exists. Hopefully these 
thoughts will start some 
BYTE readers off in a 
direction which will lead to 
commercially marketed mass 
produced software which can 
be plugged into one of the 
several microprocessor 
architectures which are on 
the market. ■ 



14 




+£& 




ks 



«jl^ i 






Join now 

Since 1947, ACM has served as the educational and 
scientific society for computing professionals— 30,000 
strong and growing. 

Write today 

For regular and student membership information 
send the attached coupon to ACM headquarters. With 
Special Interest Groups covering every major computing 
discipline and local Chapters in most metropolitan areas, 
ACM is probably the organization you're looking for. 



Association for Computing Machinery 

1 1 33 Avenue of the Americas, New York, N. Y. 1 0036 

I would like to consider joining ACM. 
Please send more information. 



Address 



City 



Zip 



The MODULAR MICROS 
from MARTIN RESEARCH 

Here's why the new MIKE 2 and MIKE 3 
are the best values in microcomputers to- 
day! 

8008 OR 8080 

Martin Research has solved the problem 
bothering many potential micro users 
.... whether to go with the economical 
8008 microprocessor, or step up to the 
powerful 8080. Our carefully designed 
bus structure allows either processor to 
be used in the same system! 

The MIKE 3 comes with an 8080 CPU 
board, complete with crystal-controlled 
system timing. The MIKE 2 is based on 
the 8008. To upgrade from an 8008 to 
an 8080, the user unplugs the 8008 CPU 
board and plugs in the 8080 CPU. Then 
he unplugs the 8008 MONITOR PROM, 
and plugs in the 8080 MONITOR 
PROM, so that the system recognizes the 
8080 instruction set. That's about it! 

If the user has invested in slow memory 
chips, compatible with the 8008 but too 
slow for the 8080 running at full speed, 
he will have to make the 8080 wait for 
memory access— an optional feature on 
our boards. Better still, a 4K RAM board 
can be purchased from Martin Research 
with fast RAM chips, capable of 8080 
speeds, at a cost no more that you might 
expect to pay for much slower devices. 

In short, the MIKE 2 user can feel confi- 
dent in developing his 8008 system with 
expanded memory and other features, 
knowing that his MIKE 2 can be up- 
graded to a MIKE 3— an 8080 system— in 
the future. 

EASE OF PROGRAMMING 

Instructions and data are entered simply 
by punching the 20-pad keyboard. Infor- 
mation, in convenient octal format, ap- 
pears automatically on the seven- 
segment display. This is a pleasant con- 
trast to the cumbersome microcom- 
puters which require the user to handle 
all information bit-by-bit, with a confus- 
ing array of twenty-odd toggle switches 
and over thirty red lights! 

A powerful MONITOR program is in- 
cluded with each microcomputer, stored 
permanently in PROM memory. The 
MONITOR continuously scans the key- 
board, programming the computer as 
keys are depressed. 

Say the user wishes to enter the number 
135 (octal for an 8008 OUTPUT 16 in- 
struction). He types /, and the right- 
hand three digits read 001. Then he 
presses 3, and the digits say 013. Finally 
he punches the 5, and the display reads 
135. Notice how the MONITOR program 
(Continued in column 3.) 



16 



QUICK.... 

what number is this? 



o o#o 



o 



If you have to read your microcomputer 
like this— bit by bit, from rows of lights— the 
computer's making you do its work. And if 
you have to use rows of toggle switches to 
program it, you might wonder why they 
call the computer a labor-saving device! 

Contrast the layout of a typical pocket 
calculator. A key for each number and 
function; six easy-to-read digits. Why not 
design microcomputers like that? 




Here they are! The modular micros from 
Martin Research. The keyboard programs 
the computer, and the bright, fully- 
decoded digits display data and memory 
addresses. A Monitor program in a PROM 
makes program entry easy. And, even the 
smallest system comes with enough RAM 
memory to get started! 

Both the MIKE 2 system, with the popular 
8008 processor, and the 8080-based MIKE 
3 rely on the same universal bus structure. 
This means that accessories— like our 450 
ns 4K RAM— are compatible with these 
and other 8-bit CPUs. And, systems start 
at under $300! For details, write for your... 

FREE CATALOG! 



MIKE 2 
MANUAL... 

This looseleaf 

book includes 

full information 

on the MIKE 2 

system, with 

schematics. 




Price for orders received 

by November 15, 1975... 

Includes a certificate worth 

a modular micro system, good 90 days. 

(Offer valid, USA only.) After H/15: $25. 



$19 

S10 towards 



^ modular micros ^ martin research ;T 



Martin Research / 3336 Commercial Ave. 
Northbrook, IL 60062 / (312) 498-5060 



shifts each digit left automatically as a 
new digit is entered! The value on the 
display is also entered into an internal 
CPU register, ready for the next opera- 
tion. Simply by pressing the write key, 
for example, the user loads 735 into 
memory. 

The MONITOR program also allows the 
user to step through memory, one loca- 
tion at a time (starting anywhere), to 
check his programming. Plus, the Swap 
Register Option allows use of the inter- 
rupt capabilities of the microprocessor: 
the MONITOR saves internal register 
status upon receipt of an interrupt re- 
quest; when the interrupt routine ends, 
the main program continues right where 
it left off. 

We invite the reader to compare the pro- 
grammability of the MIKE family of 
microcomputers to others on the mar- 
ket. Notice that some are sold, as basic 
units, without any memory capacity at 
all. This means they simply cannot be 
programmed, until you purchase a mem- 
ory board as an "accessory." Even then, 
adding RAM falls far short of a conve- 
nient, permanent MONITOR program 
stored in PROM. Instead, you have to 
enter your frequently-used subroutines 
by hand, each and every time you turn 
the power on. 

EASY I/O INTERFACE 

The MIKE family bus structure has been 
designed to permit easy addition of in- 
put and output ports. A hardware inter- 
face to the system generally needs only 
two chips— one strobe decoder, and one 
latching device (for output ports) or 
three-state driving device (for inputs). A 
new I/O board can be plugged in any- 
where on the bus; in fact, all the boards 
in the micro could be swapped around in 
any position, without affecting opera- 
tion. I/O addresses are easy to modify by 
reconnecting the leads to the strobe de- 
coder (full instructions are provided); 
this is in marked contrast to the clumsy 
input multiplexer approach sometimes 
used. 

POWER & HOUSING 

The micros described to the left are com- 
plete except for a cabinet of your own 
design, and a power supply. The basic 
micros require +5 V, 1.4 A, and — 9 V, 
100 MA. The 4K RAM board requires 
5 V, 1 A. A supply providing these volt- 
ages, and ±12 V also, will be ready soon. 

OPTIONS 

A number of useful micro accessories are 
scheduled for announcement. In addi- 
tion, the MIKE 3 and MIKE 2 may be 
purchased in configurations ranging from 
unpopulated cards to complete systems. 
For details, phone, write, or check the 
reader service card. 




The Secret of Unraveling Wire Wrap Boards 



A lot of home brew 
computer people are 
obtaining surplus printed 
circuit cards and back planes 
that have been wire wrapped. 
I n o rder to use the 
components from such 
boards the wires must be 
carefully pulled off the 
wrapping posts. Without a 
special tool it is difficult to 
remove wire while preserving 
the integrity of the delicate 
wrapping posts. Since many 
BYTE readers do not have 
the commercial dewrapping 
tools, removal of wire is for 
them a nasty and time 
consuming job at best. 

I have devised a simple 
tool which makes this task 



much easier, made from items 
normally found around a well 
equipped workshop. The 
tool, shown in Fig. 1, is 
constructed from a paper clip 
and a drapery hook. Simply 
follow the instructions. 

1. Obtain a standard 
paper clip, an Exacto knife 
holder, and a thin sharp 
pick of sorts, such as a 
drapery hook. 

2. Bend the paper clip 
and drapery hook as shown. 

3. Place the paper clip in 
the Exacto blade holder. 
Now you are ready to 
dewrap. 

4. Using the pick, flick 
the wire from the post at 
least an eighth of an inch. 




■1/8 



5. Place the paper clip bit 
onto the wire wrap post and 
slip it down until the end of 
the paper clip is just past 
the wire. 

6. Rotate the blade 
holder in the direction 
which unravels the wire 
until the entire wire is loose. 




Fig. 1. A homebuilt tool to loosen 
and remove wire wrapped 
connections. 



by 

Richard J. Lerseth 
8245 Mediterranean Way 
Sacramento CA 95826 



USE OUR HARDWARE ASSEMBLERS^ 

SAVE TIME AND FRUSTRATION WITH THESE CONVENIENT PRINTED CIRCUITS Q 

4096-BYTE MEMORY MATRIX MACRO CARD 
Have you ever wanted to construct a memory matrix as part of a system?? The tedious part is the interconnection of all the address and 
data bus pins! TheCDA-1.1 memory matrix is a general purpose memory prototyping card for the 2102/2602/9102 pinout static RAM 
chips. This PC card is 8"x10" with 70 pin edge connector, gold plated for reliability. The memory matrix occupies about 60% of 
available area with all lines brought out to pads for wire-wrap pins and has plated-through holes. The other 40% has 24 16-pin socket 
positions and a general purpose area which can hold 12 16-pin sockets, or 4 24-pin sockets, or 2 40-pin sockets. Add a custom wired 
controller to interface this board's memory matrix to any computer, or use the prewired matrix as the basis for a dedicated 4K by 8 
memory in a custom system. Think of the time you save!! 

GENERAL PURPOSE PROTOTYPING CARD 

The CDA-2.1 general purpose 8"x10" prototyping card comes predrilled for use in construction of custom circuits. This board 
accommodates 16-pin sockets plus has a general area for 16-pin sockets or 24 or 40 pin sockets. The 70-pin edge connector is gold-plated 
for reliability and the pins are brought to pads for wire-wrap post insertion. The socket side has a solid ground plane to minimize noise 
problems; busses on the wiring side allow short jumper connections for power and ground. A whole system may be constructed in 
modules with these boards. 

DIGITAL GRAPHIC DISPLAY OSCILLOSCOPE INTERFACE, CDA-3.1 

James Hogenson (see the October issue of BYTE magazine) designed a 64x64 bit-matrix graphics display for oscilloscope. This design 
permits use of your scope as a display for ping-pong, LIFE, or other games with your system. The CDA 3.1 card provides all the printed 
wiring needed to assemble the graphics display device down to the TTL Z-axis output as described in October 1975 BYTE. To complete 
the display you merely add components to this double sided card with plated-through holes. 
For info: CIRCLE READERS' SERVICE NUMBER - or, send your order using the coupon below: 



YES? 




q Please rush me the boards ordered below: 

^]4096-BVTE MEMORY MATRIX PROTOTYPING 

CARD at $39.95 
'^GENERAL PURPOSE PROTOTYPING CARD AT 

$29.95 
Q DIGITAL OSCILLOSCOPE GRAPHIC DISPLAY 

CARD AT $29.95 

LJ I've enclosed a check or money order for 
$ Foreign orders (except Canada) please 



FROM: 
NAME 
ADDRESS 



add $2 postage per card. 

Please allow four weeks for delivery 



CELDAT DESIGN ASSOCIATES 

P.O. BOX 752 
AMHERST, N.H. 03031 



you must be fully satisfied or your money will be cheerfully refunded. 



17 



HI-SPEED 

STATIC RAM 2602-1 475 ns 

Manufactured by Signetics, 2102 pinout 
$4.25 for 1/$4.00 each for 8/$3.75 each for 32 

WHY PAY FOR BEING SMALL? 

Centi-Byte is a new source of memory components 
and other necessary items for the computer hardware 
builder. Centi-Byte's function is to be a voice to the 
manufacturing companies representing you, the modest 
volume consumer of special purpose components. Centi- 
Byte brings you this special introductory offer of fast 
memory chips, chips fast enough to run an MC6800, 
MCS6501 or 8080 computer at maximum speed. These 
2602-1 's are new devices purchased in quantity and fully 
guaranteed to manufacturer's specifications. 

Centi-Byte works by concentrating your purchasing 
power into quantity buys of new components. Let me 
know what you need in the way of specialized com- 
ponents and subsystems for future offerings. With your 
purchasing power concentrated through Centi-Byte we'll 
help lower the cost of home computing. 

All orders are shipped postpaid and insured. Massachusetts 
residents add 3% sales tax. 




Carl M. Mikkelsen, Proprietor, P.O. Box 312, Belmont MA 02178 



Hidden in the matrix are 96 words and abbreviations associated with 
computers in one way or another. Find a word, circle it or color it in, 
and cross it off the list. Words may be forward, backwards, up, down, 
or diagonal, and are always in a straight line, never skipping letters. 
However, some letters are used more than once. After circling all the 
words on the list, the unused letters (14 total) will spell out a secret 
message. Beware: Some buzzwords occur in the matrix, but are not on 
the list! 

Good luck and good hunting ... it may take a while! 



















WORD HUNT 


















5 


L 


I 


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K 


E 


T 


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B 


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6 





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G 


N 


R 





N 





P 








L 


C 


A 


S 





E 


D 





C 





R 


C 


I 


M 


E 


U 


I 


I 


A 


L 


P 


H 


A 


N 


U 


M 


E 


R 


I 


C 


C 


V 


Y 


A 


L 


P 


s 


I 






ACCUMULATOR 


CHIP 


FOCAL 


MATRICES 


SOURCE 


ADD (not in address) 


CLOCK 


FORMAT 


MEMORY 


STACK 


ADDRESS 


COBOL 


FORTRAN 


MHZ 


STATUS 


ALPHANUMERIC 


COUNTER 


GATE 


MICROCODE 


STORAGE 


AND 


DATA 


GLOBAL 


MICROPROCESSOR 


SUBROUTINE 


APL 


DEBUG 


HALT 


MNEMONIC 


SUBSYSTEM 


ASCII 


DESTINATION 


INPUT 


MOS 


SYNTAX 


ASSEMBLER 


DEVICE 


INSTRUCTION 


OCTAL 


TABLE 


ASYNCHRONOUS 


DIAGNOSTIC 


INTERFACE 


PCB 


TRANSMITTER 


BASIC 


DIODE 


INTERRUPT 


PERIPHERAL 


TRAP 


BATCH 


DISK 


JUMP 


PLOT 


TTL 


BAUD 


DISPLAY 


LED 


POINTER 


VCC 


BCD 


DTL 


LINK 


PRIORITY 


VECTOR 


BET 


ECL 


LIST 


PROGRAM 


VERIFY 


BINARY 


EXECUTE 


LITERAL 


PROM 


WIRE 


BOOLEAN 


EXIT 


LOAD 


QUEUE 


WORD 


BRANCH 


FALSE 


LOCATION 


RAM (not in program) 




BUFFER 


FETCH 


LOG 


READ 




BYTE 


FILE 


LOOP 


RECORD 




CHECKSUM 


FLAG 


LSI 


ROL 





18 



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5855 Naples Plaza • Suite 301 • Long Beach, California 90803 • Telephone (213) 438-9951 



Logic Probes- 
Hardware Bug Chasers 



by 

Alex. F. Burr 

Physics Dept. Box 3D 

New Mexico State University 

Las Cruces NM 88003 



While an oscilloscope or 
voltmeter can be used with 
digital circuits, a logic 
probe is much less 
expensive if built from an 
appropriate kit. 



Digital logic, whether used 
in an 8080 microprocessor or 
as the TTL chips that can be 
used to make a processor, is, 
at least in theory, clean and 
simple because only two 
states are possible. Any point 
in even the most complicated 
circuit is either HIGH or 
LOW. However this very 
simplicity encourages the 
design of large and 
complicated circuits. While 
the chance of anything going 
wrong at any one point is 
small, the accumulated 
chances of many points 
means that sooner or later the 
experimenter is going to have 
to hunt for sources of 
trouble. 

In the case of analog 
circuits, when trouble 
develops, you get out the 
oscilloscope or voltmeter and 
start looking for places which 
have waveforms or voltages 
not meeting the 
specifications. These 
instruments can be used to 
troubleshoot digital circuits 
too. The oscilloscope is 
particularly useful if you have 
timing problems, but usually 
they give you too much 
information and may just 
confuse the issue. The 



voltmeter may tell you that 
the voltage on pin 8 is 3.9 
but, because most IC failures 
show up as a node stuck 
either HIGH or LOW, really 
all you need to know is that 
on pin 8 there is a HIGH. 
That single bit (literally) of 
information can be obtained 
with an instrument a lot 
smaller and less complicated 
than a voltmeter. 

That instrument is the 
logic probe. In its simplest 
form it is just a state 
indicator with a sharp point. 



When the point is placed on 
any pin of an IC, the probe 
will indicate whether a LOW 
or a HIGH is present at that 
point. And with digital logic 
that is usually all the 
information you need. 

Logic probes can detect a 
surprising number of 
different defective 
conditions. Fig. 1 illustrates 
some of the uses to which a 
probe can be put. Of course, 
just as voltmeters come with 
a variety of capabilities and 
prices, so do logic probes. 



SEE PULSE STREAMS 

SEE OPEN CIRCUITS 
„.OPEN BOND 




SEE LOW REP RATE 
HISHS AND LOWS 



SEE SINGLE-SHOT RESPONSES 



Fig. 1. Some of the uses of logic probes and the malfunctions which 
they can detect. 



20 



Commercial Logic Probes 

One of the first developed 
was the Hewlett Packard 
10525T logic probe. It is a 
marvel of compactness and 
versatility, all carefully 
human-engineered. Basically 
it consists of a white light 
which goes out when the 
probe is placed on a LOW and 
comes on when the probe is 
placed on a HIGH. 

Simple — yes indeed; but 
it docs much more. What if 
the point tested is open 
circuited, or the level is just 
plain bad, neither HIGH or 
LOW? Then the light glows 
at half intensity. What if a 
pulse comes along that is too 
short to excite the indicator 
light? Then a pulse stretcher 
takes over. Pulses with a 
width of between 10 ms and 
0.05 seconds are stretched to 
0.05 seconds in length. What 
if the pulses come so fast that 
the eye cannot distinguish 
one from the next? All pulse 
streams with a repetition rate 
between 10 Hz and 50 MHz 
cause the lamp to blink at a 
10 Hz rate. All this capability 
is enclosed in a probe about 
six inches long and one-half 
inch in diameter. The light is 
placed near the tip in such a 
way that it can be seen no 
matter how the probe is 
rotated. Thus you can easily 
see both the point of the 
probe and the indicator at the 




The E & L Instruments logic probe is compact, with the two indicator LEDs visible toward the 
left in this photo. 



same time. Power is supplied 
to the probe by a well 
protected single cord which is 
attached to a source of 5 V 
dc at 60 mA. 

The input impedance is 
greater than 25k Ohms in 
both the HIGH and LOW 
state (less than one low 
power TTL load). The input 
is well protected against 
operator error. The probe will 
stand ±70 volts continuously 
and ±200 volts intermittently 
as well as 120 V ac for 30 
seconds. The power input is 
internally protected from +7 
to —1 5 V dc as well as power 
lead reversal. The only catch 
is the price, which even with 
a recent reduction is $65. 

There are, however, other 
less expensive probes. Two of 



these arc distributed by E and 
L Laboratories. Their model 
340 is a logic probe and 
pulser combined into one 
instrument. The model 320 is 
a logic probe only, designed 
to give maximum information 
about the state of the node 
being tested. Both probes are 
well constructed, a little over 
6 1/2 inches in length and 
half an inch in diameter. Both 
come with two different 
probe tips and handy carrying 
cases. 

The model 340 has two 
LED indicator lights. In 
operation the two leads from 
the probe are connected to 
the 5 V dc supply and the 
probe tip applied to the IC 
lead to be tested. If that node 
is HIGH, the red LED lights 




The Hewlett Packard 10525T logic probe and 10526T pulser. 



up brightly. If that node is 
LOW, neither LED is lit. The 
green LED is used to detect 
pulses which do not last long 
enough to give a useful 
indication on the red LED. It 
lights for 0.1 seconds (just 
long enough to see) whenever 
a single pulse wider than 50 
nanoseconds is applied to the 
probe tip. In the probe tested 
for this article, when a 
voltage increasing from zero 
was applied to the tip, the red 
LED lit when the voltage was 
greater than 1.5 V; just what 
the specifications called for. 

The model 320 is a little 
more versatile as an indicating 
instrument, but it lacks the 
ability to generate pulses that 
the model 340 has. It too has 
two LED indicators, one red 
and one green. In operation, 
the two power leads are 
connected to the 5 V dc 
power supply and the tip to 
the node under test. The 
specifications say that if the 
voltage at the node is less 
than 0.7 volts the green LED 
will be lit. If the voltage is 
greater than 2.4 volts, the red 
LED will be lit. In practice 
the specifications are closely 
followed. The LEDs may 
glow dimly at voltages just a 
few tenths higher or lower 
than the specified voltages. 
But the dividing line between 
lit and not lit states is 
remarkably sharp. 

A special feature of this 
probe is the pulse storage 



21 



"Nodes" are places in a 
circuit — such as the pin of 
an IC — where you might 
want to test the logic level 
using the probe. 



capability brought into play 
by a small switch near the tip. 
When the pulse storage 
feature is on, a short pulse 
(either HIGH or LOW) is 
stretched so that it turns on 
the appropriate LED to full 
brightness even if it is as short 
as 50 nanoseconds. Square 
and sine waves appearing at a 
tested node will cause both 
LEDs to have equal 
brightness. 

The main difficulty noted 
with this probe is with the 
green LED. It is somewhat 
dimmer than the red LED 
and the lens diffuses the spot 
of light generated less well so 
that in bright room light it is 
sometimes hard to tell 
whether or not the green 
LED is lit. This fact would 
make the determination of 
the duty cycle of a chain of 
pulses by a brightness 
comparison between the 
LEDs much more difficult 
than the instruction booklet 
suggests. 

Even the E and L 
Laboratories probes are 
expensive ($35 and $25); 
although they are more 
convenient than, and 
certainly in the same price 



7 






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Fig. 2. Circuit diagram for the James logic probe kit. 



range as, a good voltmeter. 
Nothing, however, can beat 
the cost effectiveness of two 
probe kits which have been 
fairly widely advertised. 

Logic Probe Kits 

One of these kits is 
manufactured by Chesapeake 
Digital Devices. This kit 
allows one to easily construct 
a probe which uses red, green 
and yellow LEDs to signal the 
presence of logic levels in 
digital circuits. 

The kit goes together in a 
very short time with the aid 
of very complete assembly 
instructions. The whole probe 
fits into a well constructed 
case, a little over six inches 
long and slightly less than one 
inch in diameter. There are 
only three resistors, three 
LEDs, one transistor, and a 
74S00 integrated circuit to 
solder onto the clearly 
marked printed circuit board. 

In operation the green 
LED is brightly lit on a LOW, 
the red LED is brightly lit on 
a logic HIGH, while the 
yellow LED lights on an open 
circuit or a level between a 
true HIGH or LOW. A slow 
pulsing condition will be 
indicated by alternate 
flashing of the red and green 
LEDs. A fast pulsing 
condition will be indicated by 
the simultaneous activation 
of the red and green LEDs. 
The dividing line between 
these last two conditions is 
about 20 Hz, depending on 
the eye of the user. 

The biggest difficulty with 
the kit was the circuit board. 
The copper leads had not 
been tinned and were 
oxidized, making them a bit 
difficult to solder; especially 
if the builder was concerned 
that he not use so much heat 
for so long as to damage the 
components. The clear plastic 
tube into which the circuit 
board with its LEDs slide did 
crack on assembly and the 
green LED was open but 
these difficulties were easily 
remedied and the result was a 



handy logic probe at a price 
significantly less than any 
assembled probe. 

A Unique Probe 

A particularly inexpensive 
kit is the one sold by James 
Electronics for $9.95 
including postage and case. It 
is unique in that it uses a 
MAN 3 seven segment 
readout which gives a 1 for a 
HIGH a for a LOW and a P 
for a pulse train — all this in a 
compact package measuring 
five inches long and one inch 
in diameter. 

The circuit diagram for 
this intriguing probe is given 
in Fig. 2. The 2N2222 input 
transistor drives the chip, 
IC1, which in turn causes the 
appropriate segments of the 
MAN 3 to light. T he chip was 
custom made for l ames 
Electronics by National 
Semiconductor and contains 
a proprietary circuit which 
was laid down by a $500 
master mask. 

The kit comes in a very 
impressive package which was 
carefully designed to protect 
the contents from rough 
handling by the U.S. Postal 
Service. The parts, which 
include the case and a custom 
glass epoxy printed circuit 
board, are of high quality and 
are not your usual cheap 
imports. Because most of the 
parts are in the 14-pin chip 
which is the heart of the 
probe, the kit goes together 
quickly and easily for the 
experienced builder (about 
one hour to solder all the 
parts to the board). There are 
no explicit devices for 
overload or reverse voltage 
protection. The probe draws 
65 mA from any convenient 
5 V point on the circuit 
under test. 

The inexperienced builder 
is going to have trouble 
because the complete 
assembly instructions say, 
"Assemble the Logic Probe 
according to the schematic 
diagram and board layout 
shown below." The end. One 
has to have pretty sharp eyes 



22 




A logic clip is like 16 
binary voltmeters in a neat 
little package. 



A kit logic probe shown in action testing a printed circuit board. 



to orientate the IC, transistor 
and readout correctly. Even 
then you might miss the two 
jumpers that go on the circuit 
board. The circuit board also 
could have been laid out 
more efficiently so that 
the drastic bending of the 
MAN 3 leads would have 
been avoided. 

There is one serious 
defect. It is more serious 
from the theoretical than the 
practical point of view. That 
defect concerns the input 
level at which the indicator 
switches from to 1. That 
level is 0.65 volts; but the 
specifications for TTL logic 
say that the maximum 
voltage that the logic is 
guaranteed to interpret as 
LOW is 0.8 volts. Thus the 
probe would indicate a HIGH 
on a node which the logic 
would interpret as a LOW. 
This defect is of lesser 
practical importance because 
it is the unusual LOW which 
will have a voltage greater 
than 0.6 V. Indeed the usual 
gate input is only a very few 
tenths of a volt above ground 
at the most when it is LOW. 
Nevertheless it is a bit 
disconcerting to have the 
probe give a wrong reading 



even if it docs so only under 
unusual circumstances. After 
all, it is under unusual 
circumstances that the probe 
is most often used. 

Logic Clips? 

The probes which have 
been discussed so far all 
investigate one pin of the IC 
at a time. There are some 
instruments which will do 
much more. These are called 



logic clips and are not really 
probes but will give you the 
same type of information. 
They are extremely handy 
service and design tools. They 
clip onto TTL DIP ICs and 
instantly display the logic 
states of all 14 or 16 pins. 
Each of the clip's 16 LEDs 
independently follows level 
changes at its associated pin: 
A lighted diode corresponds 
to a HIGH. 



The logic clip's real value 
is in its ease of use. It has no 
controls to set, needs no 
power connections, and 
requires practically no 
explanation as to how it is 
used. The clip has its own 
gating logic for locating the 
ground and +5 volts Vcc pins 
and the buffered inputs 
reduce circuit loading. Simply 
attaching the clip to a TTL 
dual inline package makes all 




A detail of the Chesapeake Digital Devices logic probe board. The three LEDs are at the right in 
this picture, with the 74S00 IC in the center. 



23 



the logic states visible at a 
glance. The clip is, in effect, 
16 binary voltmeters. When 
used with some means of 
pulsing a complicated circuit 
slowly, sequential logic states 
like shift registers come alive 
— each state change is 
immediately visible. 

The most popular clips are 
made by Hewlett Packard and 
Circuit Specialties. 
Unfortunately they have one 
big drawback — price. They 
cost from $75 to $85 each 
and will not be discussed 
further here. 

Summary 

Table 1 summarizes all the 
information that has been 
given here and presents some 
new facts about each of the 
logic probes discussed. By 
scanning this table you ought 
to be able to determine which 
probes have the features you 
need and the ones you can 
afford. The following 
comments are based on 
personal experience with each 



of these probes, but that 
experience has been rather 
limited. 

The Hewlett Packard 
probe is obviously the best. It 
should be; it certainly costs 
significantly more. It will 
work under a wide range of 
conditions and it is carefully 
made. For the extra money 
you get wide frequency 
range, tight specifications, 
and vastly superior handling 
of pulse trains. The 
construction is first class and 
includes such extras as a 
compact BNC plug on the 
power cable (which, of 
course, is not so good if your 
breadboarding system does 
not have a BNC jack to 
supply that power). 

The E and L probes (340 
and 320) are imported from 
Japan. They are very well 
constructed and have the 
little extras like plastic 
carrying cases and different 
probe tips that the better 
Japanese manufacturers like 
to include with their 



products. The 320 is a better 
logic probe than the 340. It is 
less expensive and it handles 
pulse trains and logic levels in 
a better and more revealing 
way. Of course, it does not 
have the pulse generating 
capabilities of the 340. 

The professional logic 
designer will want to get one 
of these three probes. They 
may be a bit expensive for 
the serious hobbyist. In that 
case one of the two kits 
would be satisfactory. 

Both kits went together 
easily and rapidly. The CDD 
kit is much more revealing 
about the state of the logic 
under test and has superior 
assembly instructions. The 
James kit has better quality 
parts and is cheaper. 

In any case the serious 
worker in digital logic and 
computers, whether a 
professional or a serious 
hobbyist, will find one of 
these probes a valued 
addition to his collection of 
test equipment. ■ 



Table 1. Characteristics of logic probes. 






1 




Probe 


HP 10525T 1 


340 2 


320 2 


CDD 3 


James 


Operating 


5 ± 1 0% V 


5 ± 1 0% V 


5 ± 1 0% V 


5 ± 1 0% V 


5 V 


Voltage 












Current 


60 mA 


100 mA 


80 mA 


40 mA 


65 mA 


Frequency 


50 MHz 5 


12MHz 


12MHz 






Response 












Input Impedance 


>25 k£2 


BOkfll 


1 00-600 kS2 






Min. pulse width 


10 ms 6 


50 ms 


50 ms 




See 11 


Levels OPEN 


half intensity 


no lights 


no lights 


yellow 10 




HIGH 


on >2±0.2 V 


red>1.5 V 


red > 2.4 V 


red >2.5 V 


1>0.7 V 


LOW 


^ +0.2 
off <0.8 ' " V 
-0.4 


no lights 


green <0.7 V 


green <Cl V 


0<0.7 V 


Size 


6" x 0.5" dia. 


6.6" x 0.6" dia. 


6.6" x 0.6" dia. 


6" x 1" dia. 


5x1" dia. 


Overvoltage 


excellent 


reasonable 


reasonable 


none 


none 


protection 












Price 


$65 


$35 8 


$25 


$15 12 


$10 12 



Notes: 

1 Hewlett Packard, Palo Alto CA 94304. 

2 E and L Instruments Inc., 61 First St., Derby CT 06418. 

3 Chesapeake Digital Devices, Inc., Box 341, Havre de Grace MD 21078. 

4 James Electronics, Box 822, Belmont CA 94002. 

^Pulse trains faster than 10 Hz cause the lamp to flash at a 10 Hz rate. 

"Pulses between 10 ms and 0.05 seconds are stretched to 0.05 seconds. 



7 Short pulses indicated by green LED. 

"Single pulse generator contained in probe. 

^Switchable pulse stretcher for short pulses. 

10 Yellow LED is also lit if voltage is between HIGH and LOW. 

11 Indicator reads P for pulse trains 5* 20 Hz. 

1 ^Kit price. 



24 



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change without notice. 



25 



Powerless IC 
Test Clip 



circuit by 
John Errico 
5 Richard Rd. 
Hudson MA 01749 

written by 
Robert Baker 
34 White Pine Dr. 
Littleton MA 01460 




This test clip operates like 
the expensive, commercially 
available clips selling for $85 
or more without requiring 
batteries or external power. 
All types of ICs may be 
tested (TTL, DTL, MOS, etc.) 
and LEDs are used to indicate 
the logic state of each pin 
being tested. 

The heart of the test clip is 
a Texas Instruments TIDI25 
diode array which costs about 
$3.75. Two diode arrays are 
used to determine the pin 
with the highest voltage (Vcc) 
and the pin with the lowest 
voltage (ground). These pins 
are then used to power the 
LEDs on the test clip itself, 
thus taking power from the 
IC on the board and 
eliminating the need for an 
external or separate supply. 
The circuit is straight forward 
and may be expanded to 
make a 24- or 40-pin test clip. 
The larger test clip, however, 
may be difficult to use due to 
the size of the LED display. 

The basic IC clip is a 
standard item available from 
AP Products Inc., Box 110-Z, 
Painesville OH 44077. The 
16-pin clip is part number 
923700 (TC-16) and sells for 
$5.75 each. 



26 



The diode arrays are 
14-pin dip packages and were 
chosen to make the test clip 
more compact. To cut down 
the cost, 16 general purpose 
silicon diodes may be used in 
place of each diode array IC. 
The transistors used to drive 
the LEDs may be any NPN 
transistor capable of handling 
the LED current. Any small 
size LED may be used; 
however, the 1k resistance 
value may have to be 
changed. Choose a value 
which gives about 2 mA 
current through the LED; this 
should give sufficient 
brightness without loading 
down the circuit supply. 

Construction is very 
simple and parts layout is not 
critical. Use a small piece of 
0.1" grid perforated board 
bolted to each side of the IC 
clip to mount components 



on. Try to keep the overall 
physical size of the boards as 
small as possible to make the 
finished test clip easier to 
handle. The LEDs should be 
mounted along the top edge 
of the perforated boards so 
they are visible from above 
the clip when it is attached to 
an IC. I would suggest 
wrapping a small piece of 
dark tape or using a short 
piece of dark tubing around 
each LED to improve 
visibility of the finished LED 
display. One of the TID125 
diode arrays is mounted on 
each piece of perforated 
board along with the 
associated resistors and 
transistors, positioned 
wherever convenient. 
Remember to run two wires 
between the two perforated 
boards to connect the Vcc 
and ground outputs of the 



diode arrays together. These 
wires should be stranded to 
withstand the movement of 
opening and closing the test 
clip when in use. 

Using the test clip is the 
simplest part of all. Just clip 
it over the desired IC. Don't 
worry about how to position 
the test clip on the IC; pin 1 
may be at either end and the 
test clip will still work 
properly. With the test clip 
installed on an IC package the 
LEDs will indicate the logic 
level of each pin: 

ON = Logic 1 (HIGH) or Vcc 

pin 

OFF = Logic (LOW) or 

ground pin 

On 14-pin ICs disregard the 
two pins not attached. 

Who said building an IC 
test probe is hard? ■ 



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• »■ V^' 














/" "\ MV5054 -2 










fir) or 




























































1 




— « 


» 2 i 


? i 


P J 


7 i 


> 8 i 


? < 


»" -i 


GND 
12 

i' -V 




i 3 


7 




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i 


k 


1 


I 


1 

< 

1 


> 

k" 


7 


I 


7 

< 


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• "" v cc ALL RESISTORS = 1/8 WATT 
: CONNECT ALL V cc PINS 
1 TOGETHER 8 ALL GND 
PINS TOGETHER 

Fig. 1. Powerless IC Test Clip. 
































1 



TIDI25 DIODE ARRAY 



27 



HARDWARE ! 

Wb have Altair compatible plug-in peripherals! 



BUILD A SMART TERMINAL INTO YOUR 
ALTAIR! Your Altair 

already has Ihe intelligence, we provide the display 
module. This module is not a limitied "TV Typewriter" 
but an ultra-high speed computer terminal built into 
your computer. The VDM-1 generates sixteen 64 charac- 
ter lines from data stored in the IK byte on-card 
memory. Alphnumeric data is shown in a 7x9 dot matrix 
format with a full 128 upper and lower case ASCII 
character set. The VDM-1 features EIA video output for 
any standard video monitor, multiple programmable 
cursors, automatic text scrolling and powerful test 
editing software included FREE! Available now. 

!! MASS STORAGE !! 

We have always wanted a low cost, reliable, fast access 
storage device using standard Phillips cassettes (we bet 
you have too), so we got to work and designed one 
here it is! With the CDS-VIII Cassette Data System you 
have computer controlled access to I 28K bytes of data 
within 20 seconds when using C-30 cassettes. We provide 
read/write electronics and transport controller, Altair 
interface, a case and power supply, and one or two 
multiple motor cassette transports plus FREE driving 
software! Yes, up to two cassette drives! Two drives 
provide much more powerful file handling and copying 
capabilities as well as, of course, twice the storage 
capacity. Data can be written and/or read asynchronous- 
ly at any transfer rate up to 150 bytes/sec: at this rale 
8K BASIC can be loaded in about 50 seconds! We have 
also included provision for use of any read/write 
electronic plug-in section so that tapes using HIT, 
Computer Hobbyist or Digital Group formats may be 
read at lower data rates. Available in November 1975. 

4KRA Static Read/Write Memory 

This 4096 word STATIC memory provides faster, more 
reliable and less expensive operation than any currently 
available dynamic memory system. The 4KRA permits 
Altair 8800 operation at absolute top speed 
continuously. All RAM's (Random Access Memories) 
used in the 4KRA are 91L02A's by Advanced Micro 
Devices, the best commercial memory 10 on the market 
today. 91L02A's require typically 1/3 the power of 
standard 2102 or 8101 type RAM's and each one is 
manufactured to military specification MIL STD-883 for 
extremely high reliability. These memories can be 
operated from a battery backup supply in case of power 
failure with very low standby power consumption. (Ask 
for our technical bulletin TB-101 on power down 
operation.) In short we have done everything we could 
to make the best 4K memory module in the computer 
field, and because we buy in large quantity, we can make 
it for a very reasonable price. Available now. 

2KRO Erasable Reprogrammable 
Read Only Memory Module 

With this module the Altair 8800 can use 1702A or 
5203 type Erasable Reprogrammable ROM's. The7KR0 
accepts up to eight of these IC's for a capacity of 2048 
eight bit words. Once programmed this module will hold 
its data indefinitely whether or not power is on. This 
feature is extremely useful when developing software. 
All necessary bus interfacing logic and regulated supplies 
are provided but NOT the EPROM IC's. Both 1702A 
and 5203 PROM's are available from other advertisers in 
this magazine for well under $25. Available now. 



3P+S Input/Output Module 

Just one 3P+S card will fulfill the Input/Output needs of 
most 8800 users. There are two 8-bit parallel input and 
output ports with full handshaking logic. There is also a 
serial I/O using a UART with both teletype current loop 
and EIA RS-232 standard interfaces provided. The serial 
data rate can be set under software control between 35 
and 9600 Baud. You can use your old model 19 TTY! 
This module gives you all the electronics you need to 
interface most peripheral devices with the Altair 8800, 
it's really Ihe most useful and versatile I/O we've seen 
for any computer. Available now. 

MB-1 Mother Board 

Don't worry any more about wiring hundreds of wires in 
your Altair to expand the mainframe. Our single piece 
1/8-inch thick, rugged mother board can be installed as 
one single replacement for either three or four 88EC 
Expander cards, so you don't have to replace your 
already installed 88EC card if you don't want to. The 
MB-1 has very heavy power and ground busses and 
comes with a piece of flat ribbon cable for connection to 
the front panel board of the 8800, a built-in bus termi- 
nator, and card guide cage for sixteen plug-in slots. 
Available now. 



Item 



PRICE LIST effective Oct. 1, 1975 

Kit Assembled Delivery 



2KRO EPROM module 
3P+S I/O module 
4KRA-2 RAM module w/ 
2048 8-bit words 
4KRA-4 RAM module w/ 
4096 8-bit words 
RAM only, AMD91L02A 
500 nsec, LOW POWER 
CDS-VIII-1 Cassette Data 
System w/one transport 
CDS-VIII-2 w/two trans- 
ports 

MB-1 Mother board, bus 
terminator, card cage 
VDM-1 Video Display 
module 



$ 50. S 75. 3 weeks max. 
125. 165. 3 weeks max. 

WRITE FOR DETAILS 

WRITE FOR DETAILS 

8/S40. - 3 weeks max. 

WRITE FOR DETAILS 

WRITE FOR DETAILS 

70. — 3 weeks max. 

160. 225. 3 weeks max. 



TERMS: All items postpaid if full payment accompanies 
order. COD orders must include 25% deposit. 
MaslerCharge gladly accepted, but please send us an 
order with your signature on it. 

DISCOUNTS: Orders over $375 may subtract 5%; orders 
over $600 may subtract 10%. 



E Processor Technology 
2465 Fourth Street 
Berkeley,Ca.947K> 

(415) 549-0857 



:♦:<•• 



SOFTWARE ! 



WE HAVE ALTAIR COMPATIBLE 8080 SOFTWARE AND FIRMWARE MODULES! 

If you haven't used our Assembly Language Operating System you have been missing 
a wonderful experience. We have found the ALOS Resident Editor and Assembler to be 
an extremely useful and powerful program development tool. We are so sure you will be 
turned on with our Software Package No. 1 that we are practically giving a listing away for 
a mere S3.00US. Yes, this is a source listing as well as a hexidecimal printout. 

The Assembly Language Operating System gives you the ability to write programs in 
8080 Assembly Language with labels, expressions and comments. The programs can then 
be edited by line number, a powerful feature that makes corrections and additions very 
easy. The program can be named as a file and stored at a user selected memory location 
while another file is being worked on. Files can be listed by line number using the LIST 
command before being assembled. The Assembler converts the Assembly Language 
mnemonic codes and labels to hexidecimal op-codes at any address selected by the user 
to run at any address (the run address may be different from the location in memory 
where the program is placed). Assembly can be performed with or without error 
messages being printed. After assembly the program can be run using the EXECUTE 
command or dumped onto cassette or paper tape using the DUMP command. 

Paper tapes or cassettes of the program listing will not be available to individuals but 
we have already sent paper tapes to several computer clubs around the country. We 
suggest you contact one of the clubs if you want a copy of the tape or need assistance. 
We will be happy to send tape copies to any bona fide "amateur" computer club or 
society, so if you are a member of such a group, please let us know of your group's 
existence by sending us a copy of its latest newsletter. 

In addition we have a manual describing the use of the ALO System from the ground 
up. This will include a complete description with examples of every command, instruc- 
tions on the use of all internal routines by other programs and an overview of efficient 
file generation and handling. 

An even more wonderful version of the ALOS is available in firmware as part of an 
8K PROM module. The expanded version allows dynamic Input/Output allocation, file 
area management by the executive, octal and/or hex data entry, loaders for both 8800 
BASIC and Intel Ilex Format tapes, and many other capabilities not included in the 
original Package No. 1. The basic Resident Executive-Editor-Assembler occupies about 
4K of the 8K maximum capacity. So why the 8K?? Because we are leaving space for 
future expansion. The first expansion is a powerful Simulator that adds-on to the basic 
ALOS package. 

SIMULATOR'.'? Yes, an Interpretive Simulator which runs 8080 programs on the 
same 8080 that contains the Simulator! Not just traps and breakpoints but simulated 
I/O, registers, flags, program counter and stack pointer. Any of these can be modified at 
all times; plus a single step mode that displays all the registers, pointers, flags, etc., after 
execution of each instruction. This Simulator is the most powerful debugging tool for 
the 8080 that we know of. Just think, you will hardly ever again have to touch the front 
panel switches. 

Both versions of our ALOS require 2K bytes of RAM for system internal storage and 
symbol tables. In addition at least 4K more is needed to hold user files, although greater 
capabilities are achieved with 8K or 12K of user space. 



PTCOS! 



What is PTCOS you may ask?? It stands for Processor Technology Cassette Operating 
System and it means a real Operating System program based around our CDS-VIII dual 
Cassette Data transport System. When operating under this program you have true file 
handling power to create, delete, edit, relocate, and copy all kinds of files (e.g. BASIC 
and programs written in BASIC). PTCOS can handle multiple I/O devices using a special 
type of file and suitable small driving routines. At last an integrated system concept for 
the 8800 is a reality! PTCOS is devilishly similar in its basic operation to an FDOS and is 
upward compatible with future software developments from Processor Technology. 

PRICE LIST effecitve OCT. 1, 1975 

KIT ASSEMBLED DELIVERY 



Assembly Language 1 24o5 FOUfth Street 



Software package No. 1 

Assembly Language 

Operating System $3.00 3 weeks max. 

PTCOS: Processor 

Technology Cassette 

Operating System WRITE December '75 

ALS-8 PROM Firm- 
ware module expanded 
version of SP No. 1 $275. $325. 3 weeks 

SIM-1 PROM Firm- 
ware add-on to ALS-8: 
Simulator section $95. $110. 3 weeks 



E Processor Technology 
2465 Fourth Street 
Berkeley,Ca.94710 

(415) 549-0857 



What is a Character ? 



by 

Manfred Peshka 
Peterborough NH 03458 



A character is a unit of 
information used in a com- 
munication between a sender 
and a receiver. Senders and 
receivers may be either 
people or machines, or a mix 
of the two. A character may 
be represented in different 
forms: People use mostly 
graphics, such as the letters of 
the alphabet, the digits or 
occasionally the Roman 
numerals, and the punctua- 
tion and special symbols 
which are So familiar to us. 
Machines process a set of 
electric pulses in a period of 
time which normally repre- 
sents a character. This time 
period differs in length for 
different devices; it is longer 



for slow devices (terminals, 
card readers, printers) than 
for fast devices (tape and disk 
drives), and is generally the 
shortest for the computer 
arithmetic and logical unit. 

Parenthetically it should 
be noted that some machines 
can recognize graphics, draw- 
ings, and even objects (units 
providing information) in a 
landscape. The discussion of 
these machines, however, is 
reserved to a future article, 
and their cost is far beyond 
that of the amateur and 
hobbyist at the present time. 

Symbolic Representation of 
Alternatives 

What is the minimum 
number of information ele- 
ments, characters, or basic 
symbols needed to express an 
alternative? Probably the 
most common symbol is the 
indicator light which tells us 
that a system is in a specific 
state as opposed to its 
"usual" state. Let's consider 



for a moment the sign "Fire 
Trucks Entering on Blinking 
Red Light." This sign indi- 
cates the possibility of two 
specific states: The "usual" 
state prevails when fire trucks 
are either on a call or waiting 
in the garage; in this situation 
the light is off. The alterna- 
tive consists of an emergency 
when the light is blinking to 
inform people that trucks are 
about to enter the street, or 
just have entered and are 
rushing to the fire. Thereafter 
the light is again turned off. 
The light is pulsing for a 
period of time which nor- 
mally represents this 
particular situation or "unit 
of information," say, about 
20 seconds. 

The indicator light 
actually represents the 
simplest character or basic 
symbol providing a unit of 
information. It is binary 
telling you that a given situa- 
tion either prevails or not. 
Similarly, the door bell, the 



telephone bell, the oil 
pressure light on your car, 
etc., are binary symbols. 
Binary means nothing else 
but a characteristic, property, 
or condition of a system in 
which there are but two alter- 
natives. Besides indicator 
lights, bells, etc., binary 
symbols can take on graphic 
forms such as yes or no, true 
or false, 1 or 0, to name a few 
only. For a machine, the 
form is either the absence or 
presence of a certain elec- 
trical energy level at a period 
of time of specific duration. 
While the duration of 
signaling or "marking" in the 
case of the oil indicator light 
may be variable depending on 
engine rotation, pressure, 
temperature, etc., it is 
constant for computing 
machines. It may be a 
1/1 10th or 1 /300th of a 
second for a slow terminal, or 
a billionth of a second foi* a 
computer central processing 
unit. 



30 



Binary and Ternary Symbol 
Sets 

We have seen that one 
binary character suffices to 
indicate two distinct states. 
On the other hand, an 
elevator is in one of three 
states: It is idle, or it is going 
up, or it is going down. 
Naturally one binary symbol 
is not enough to represent 
three states. Two lights may 
be used as follows: The left 
light may signal upward 
motion when illuminated, 
and the right light may signal 
downward motion. No 
upward or downward motion 
is indicated when the 
corresponding light is turned 
off. Let's represent the two 
possible states of the 
indicator lights by the 
graphics 1 of on and for 
off. The following three 
characters then express the 
three possible states: 



00 


[ 00 ] 


idle 


01 


[ o*. ] 


down 


10 


[ *o ] 


up 



Note that a character, that is, 
the unit of information, is 
represented by two bits or 
binary digits. We now have 
used a two-bit character code 
to symbolically represent the 
states of the system 
consisting of the elevator and 
its two lights. 

An entirely different way 
to represent three distinct 
states symbolically is 
accomplished by increasing 
the number of basic symbols 
from two to three. Let's use 
the graphic 2 to indicate 
upward movement. Instead of 
the left and right indicator 
lights, such conditions may 
be indicated by a panel 
displaying the terms idle, 
down, or up as follows: 



This time we used a code 
consisting of ternary digits to 
symbolically represent the 
three states of the elevator 
and its indicator panel. 
Ternary means that a 
characteristic, property, or 
condition of a system can 
prevail in one of three 
alternatives. 

Note that the unit of 
information, or in other 
words, the character, has 
been coded in the first case 
by two binary digits, and in 
the second instance by one 
ternary digit. One can 
conceptualize a character as a 
distinguishing mark indicating 
a specific state of a system. 
Characters are "marks of 
distinction" which may be 
represented in different 
graphic forms which have 
equivalent value: 



Binary Ternary Implementation 

00 [ oo ] [ IDLE ] 

01 1 [ 0*1 j | DOWN] 
10 2 [ -fco ] [ UP | 



The two bit code permits a 
fourth alternative, namely 11. 
In actuality, this situation 
represents a contradiction 
since the elevator cannot 
move up and down at the 
same time. However, this 
character may be used to 
signal a defect, such as the 
elevator being stuck between 
two floors, or it may simply 
be out of operation. The 
ternary code cannot signal 
this condition unless an 
additional basic symbol is 
being used; let's assume that 
an additional panel indicates 
a defect when illuminated, 
and the code representing this 
situation consists of a binary 
digit concatenated with a 
ternary digit as follows: 



In this situation, the 
character or information unit 
is represented by one binary 
and one ternary digit. It is a 
mixed code, principally 
similar to those found on 
license plates consisting of 
letters and decimal digits. 

In this situation, two of 
the six possible characters 
remain unused, namely 11 
and 1 2. At least, let's hope 
that they remain unused 
because 11 would mean that 
a defective elevator is in 
downward motion. 

Enumerating Alternatives 

The number of alternatives 
which need to be considered 
in a given system determines 
the coding requirements. The 
more alternatives need to be 
communicated, the more 
"marks of distinction" are 
required. We have seen the 
two basic ways to accomplish 
this: Increase the number of 
distinguishing graphics in the 
character set, or concatenate 
graphics from the same or 
from different sets of basic 
symbols to form strings. 

Obviously there is some 
upper limit to the number of 
distinguishing marks available 
to people. Humans have a 
limit of what they can 
comfortably memorize in 
terms of numbers of basic 
symbols when there is no 
specific meaning attached to 
them. Consequently there 
comes a point when graphics 
are being concatenated to 
form symbol strings which 
represent words. The string 
3-D stands for the word 
which we pronounce 'thre-'de 
and which obviously means 
"the three-dimensional form 
or a picture produced in it" 
(Webster's Seventh New 
Collegiate Dictionary 1965: 
page 920). We use the 
decimal digits 0, 1, 2, . . ., 9 
to represent numbers, the 
letters a, b, c, . . ., z, A, B, 






1 IDLE ] 


neither down 


10 






nor up 


00 


1 


|DOWN ] 


down 


01 


2 


1 UP ] 


up 


02 



[ DEFECT 



IDLE 

IDLE 

DOWN 

UP 



31 



. . ., Z to represent the 
alphabet for words; special 
symbols and punctuation 
marks are concatenated with 
digits and letters to form even 
longer strings to represent 
expressions which inform 
people about one specific 
alternative out of, say, a 
million possibilities. We form 
mathematical expressions 
(x 2 +x— 3, etc.) and word 
expressions (i.e., sentences) 
and a combination of the 
two: "Yesterday it rained in 
Peterborough for two hours." 

The basic unit of 
information is the basic 
graphic symbol or character: 
The space on the paper, the 
special marks (+ — <,; etc.), 
the letters, and the decimal 
digits, and, which is not 
immediately obvious, certain 
functions like the bell on the 
typewriter which signals the 
approach of the right margin, 
the backspace, the margin 
release, the carrier return, the 
line feed adjustment, etc. The 
latter group is called 
functions or control 
characters. In the computer 
and communications field 
many more functions are 
encountered than there are 
on the typewriter. These will 
be discussed in detail further 
on. 

The number of graphics 
available for marking one out 
of many possible states of a 
system is referred to by the 
name base. Digits are used to 
represent numbers; since 
people generally use ten 
distinct digits, the number 
system is called a decimal 
system. The base of this 
system is 10. In the previous 
section the binary number 
system and the ternary 
system were used. Their bases 
are two and three, 
respectively. 

Using any one of these 
systems, it is possible to mark 
any number of alternatives. If 
the number of alternatives 
exceeds the base (i.e., the 
number of distinct graphics in 
the set) one or more 
additional graphics are used. 



TabJe J. Equivalence of Selected Graphics. 



Binary 



1 

10 

11 

100 

101 

110 

111 

1000 
1001 
1010 
1011 
1100 
1101 
1110 

1111 

b= 2 
g= 4 
a= 16 



Ternary 


1 
2 

10 

11 

12 

20 

21 

22 
100 
101 
102 
110 
111 
112 
120 

3 

3 

27 



Octal 



1 

2 

3 

4 

5 

6 

7 
10 
11 
12 
13 
14 
15 
16 
17 

8 

2 

64 



As an example, let's assume 
that we desired to mark any 
one of sixteen alternatives. If 
we used the letters to mark 
these possibilities, as is often 
found in term papers and 
legal documents to mark 
paragraphs and sections, one 
graphic for each alternative 
would suffice. As a matter of 
fact, out of the 52 available 
letters only sixteen would be 
used. Thirty-six graphics 
would not be used. Two 
decimal graphics are required 
to express sixteen options, 
leaving 84 pairs unused. 
Three ternary graphics 
encompass these sixteen 
possibilities leaving eleven 
triplets unused. A quadruplet 
of binary graphics generates 
exactly sixteen possibilities. 

In general, by using 'g' 
graphics of a set with base 'b', 
the maximum number of 
alternatives 'a' is determined 
by multiplying 'b' with itself 
for 'g' times, or in other 
words, a=b§. Table 1 
summarizes this rule by 
enumerating all possible 
arrangements of binary, 
ternary, octal (base 8), 
decimal, and hexadecimal 
(base 16) graphics for the 
first sixteen values or 
alternatives. 

To illustrate the rule to 
calculate the maximum 
number of alternatives, the 
hexadecimal system requires 



Decimal 



1 

2 

3 

4 

5 

6 

7 

8 

9 
10 
11 
12 
13 
14 
15 

10 

2 

100 



Hexadecimal 


1 
2 
3 

4 
5 
6 

7 
8 
9 
A 
B 
C 
D 
E 
F 

16 

1 

16 



only one graphic (g=1) for a 
maximum of sixteen 
alternatives (a=16) because its 
base equals sixteen (b=16). 
Note, however, that the 
largest value or number 
equals fifteen which is 
represented by the graphic F 
because enumeration began 
with the magnitude zero. 

The maximum value is 
always one less than the 
number 'a' because these 
systems start counting with 
zero. Assuming two 
hexadecimal graphics (g=2), 
256 distinct alternatives can 
be identified (a=16 2 ). The 
largest value, however, is 
equal to 255 (a— 1) because 
the first value is zero. The 
hexadecimal string FF 
identifies the same magnitude 
as the decimal string 255 or 
the bit string 11111111. 

It is easy to change from 
one coding system to 
another, especially from 
binary to hexadecimal and 
back, by means of Table 1. 
The choice of the 
hexadecimal graphics A to F 
was arbitrary and is of great 
help to people. Machines 
represent all characters as 
binary pulses within a given 
time period. Bit strings, 
therefore, can become very 
large and difficult to 
remember. Imagine the bit 
string 10001111011100. 
How much easier it is to 



32 



remember the hexadecimal 
string 23DC instead (you may 
wish to verify the translation 
starting with the right four 
bits). Any other distinct 
graphics instead of A to F 
could have been used; for 
example ! @ # < % >. 
However, try to remember 
these in this order, and try to 
pronounce 23<# instead of 
the above 23DC. 



How to Identify Character 
Sets 

Given the possibility of 
switching from one 
representation to another, the 
question of code 
identification must be dealt 
with. Assume the graphic 
representation 3-D. Is it a 
word of the English language? 
Or is it an arithmetic 
expression? If it is an 
arithmetic expression, which 
number system has been 
employed? Assume another 
representation such as 11. 
Which number system has 
been employed and what 
magnitude is represented? 
You may wish to consult 
Table 1 and calculate the 
magnitude for each number 
system. 

In order to avoid 
confusion, graphics other 
than decimal digits, letters, 
and the special symbols are 
identified explicitly. The 
string 1 1 therefore means 
eleven in the decimal number 
system, and 3-D is part of the 
English language. If a ternary 
string was meant, one needs 
to say so in some 
unambiguous manner. This 
can be accomplished through 
a textual declaration such as 
"All following digits are 
ternary digits" or, "The 
ternary number 11 has a 
value of 4" where according 
to our convention the graphic 
4 is understood to be a 
decimal digit. 

A different way to 
identify strings is by 
appending to the string the 
base. In the mathematical and 
computing literature different 
methods have been 



employed. In the 
mathematical literature, this 
is accomplished by a separate 
graphic which is appended to 
the digit string: 112 is a 
binary number with a value 
of three, while 1 1 8 is an octal 
number representing nine, 
and 1 1 16 is a hexadecimal 
number representing 17. The 
subscripted graphic represents 
the base, and it is omitted 
whenever the base is ten. This 
convention also avoids the 
confusion about 3-D. This 
string is an expression of the 
English language, whereas 
3-Di6 equals 3-13 or — Ai6 
which is a numeric expression 
resulting in a number. 

In the computing 
literature, different ways have 
been found to identify bit or 
hexadecimal strings. These 
ways depend on the 
manufacturer and on the 
computing language 
employed. In American 
National Standard (ANS) 
Fortran, a predominately 
mathematical language 
(which is to be distinguished 
from Basic Fortran), digit 
strings are recognized as 
decimal numbers. Bit strings 
are not allowed, and non-digit 
strings as used for headlines, 
table headings, etc., are 
preceded by one or more 
digits and the capital letter H; 
for example, 4H3.14 means 
the four characters 3.14 
which differ in their internal 
representation from the 
magnitude 3.14. The constant 
4 prior to the H indicates the 
length of the string; it is four 
symbols long. 

In ALGOL 60 which is an 
internationally standardized 
mathematical language, digit 
strings are recognized as 
decimal numbers, and 
character strings for table 
headings, etc., are enclosed in 
so-called string brackets as 
shown in the example: '. . . 
The wife stated that her 
husband told her 'our 
daughter complained 'the 
teacher is giving me trouble'". 
Note that it is possible to 
have strings within strings, 
each of which is enclosed by 



the single quotes pair. 

In Programming Language 
One (PL/I), as devised by 
IBM, digit strings are 
recognized as decimal 
numbers unless they are 
appended by the letter B. 
11B equals 11 2 and has a 
value of 3. Since the internal 
representation of binary 
numbers differs from codes, 
this language also permits 
explicit bit and character 
strings such as '11'B which 
does not necessarily have a 
value of 3 but could mean, 
for example, that the elevator 
is out of order. Alphanumeric 
character strings are also 
permitted and recognized 
whenever they are enclosed in 
single quotes: 'THIS IS A 
"STRING", ISN'T IT?'. 
Similar distinctions exist also 
in ALGOL 60 and will be 
discussed in a future article. 

You might have noted that 
the character constants in 
Fortran were preceded by the 
length indicator and an 
identifying character H. In 
the systems using quotes or 
string brackets, the length is 
determined by the number of 
positions occupied between 
the brackets. Many assembler 
languages combine these two 
methods. The string is 
enclosed in quotes, and it is 
preceded by a single letter 
indicating the base. B'1V is 
equal to 11B or '11'B and has 
a value of 3 when it is used as 
a number in integer 
arithmetic. X'1 V equals 11 16 
or 17 and is a hexadecimal 
string. 

The distinction between 
binary numbers and bit 
strings is a rather fine one and 
will be discussed in a future 
article. The computer 
represents all information as 
strings of bits and 
manipulates these strings 
according to their type in 
certain groupings of bits. The 
basic group is called a 
machine word and consists of 
one or more bits. These bit 
groups have an equivalent 
code value which can be 
represented graphically in 
several different ways. 



33 



Function Abbreviations 

We have discussed earlier 
various functions of the 
typewriter. Computer 
terminals and communica- 
tions equipment use many 
more function characters 
than the common typewriter 
does. In the various codes, 
these functions correspond to 
certain bit strings. The 
functions are indicated in the 
code tables on the following 
pages by abbreviations. 
Therefore, in Table 2 a 
dictionary of these 
abbreviations is presented. 

The more frequently 



encountered terminal 
function codes (as opposed to 
transmission functions) are 
marked with an asterisk. 

The Baudot Five-Bit 
Telegraphy Code 

An operator depressing the 
telegraph key causes current 
to flow through a wire. The 
current actuates an 
electromagnet at the receiving 
end which produces a 
"click". The timing between 
the clicks represents either a 
dot or a dash, and 
telegraphers yesterday, and 
hams today, are skilled in 



Fig. J. The word BYTE in Baudot Code. 



"MARKING" 



SPACING 



LETS — 
I — I— I — i- 





I START ST OP I 




W-ONE CHARACTER— H 




— H I I- 5 -t I.5 I 




OR 




TIME UNITS 1. 42 


Table 2. Function Abbreviations. 


ACK 


Affirmative Acknowledgement 


BEL, BELL Bell or other audible signal 


BS 


Backspace 


BYP 


By Pass 


CAN 


Cancel 


CC 


Cursor Control 


CR 


Carriage Return 


CU1 


Customer Use 1 


CU2 


Customer Use 2 


CU3 


Customer Use 3 


DC0 


Device Control 0. 


DC 1 


Device Control 1 


DC 2 


Device Control 2 


DC 3 


Device Control 3 


DC 4 


Device Control 4 (stop) 


DEL 


Delete 


DLE 


Data Link Escape 


DS 


Digit Select 


EM 


End of Medium 


ENQ 


Enquiry 


EOA 


End of Address 


EOB 


End of Block 


EOM 


End of Message 


EOT 


End of Transmission 


ERR 


Error 


ESC 


Escape 


ETB 


End of Transmission Block 


ETX 


End of Text 


FE 


Format Effector 


FF 


Form Feed 


FIGS* 


Figures Shift 


FS 


Information File Separator 


GS 


Information Group Separator 


HT 


Horizontal Tabulation 


IDLE 


Null 


IFS 


Interchange File Separator 


IGS 


Interchange Group Separator 


IL 


Idle 



translating these "dots" and 
"dashes" into graphics. 

Transmission speed was 
mostly dependent on the 
telegraphers' skills. The term 
"baud rate" means the 
frequency at which the dots 
recurred in a second, with 
every dash counting twice as 
long as a dot. 

In the automatic 
teletypewriter the key was 
replaced by a distributor 

which sends a fixed number 
of pulses for each character 
entered on a keyboard. 
Latches at the other end 
actuated a printing device. 



The term "marking" was used 
to indicate the flow of 
current, and the line was 
"spacing" when the current 
was off. Marking and spacing 
can be related to binary 
digits. In Table 3, a mark is 
indicated by the bit 1, and a 
space by the bit 0. In 
addition to the five bits of 
the code, a space occurred 
prior to transmission, and a 
longer mark (1.5 or 1.42 
times the usual mark time) 
terminated the code. Fig. 1 
shows the timing of marks 
and spaces of the string 
BYTE: 



IRS 

ITB 

I US 

LC 

LETS 

LF 

NAK 

NL 

NUL 

PF 

Pl\l 

PRE 

RES 

RS 

RU 

RVI 

s -s 7 

SI 

SK 

SM 

SMM 

SO 

SOH 

SOM 

SOS 

SP 

STX 

SUB 

SYN 

TM 

TTD 

UC 

US 

VT 

VTAB 

WACK 

WRU 



Interchange Record Separator 

Intermediate Text Block 

Interchange Unit Separator 

Lower Case 

Letters Shift 

Line Feed 

Negative Acknowledgement 

New Line 

Null, or all zeros 

Punch Off 

Punch On 

Prefix 

Restore 

Record Separator (Reader Stop) 

Are you . . . ? 

Reverse Interrupt 

Separator Information 

Shift In 

Skip (punched card) 

Set Mode 

Start of Manual Message 

Shift Off or Shift Out 

Start of Heading 

Start of Message 

Start of Significance 

Space 

Start of Text 

Start of Special Sequence 

Synchronous Idle 

Tape Mark 

Temporary Text Delay 

Upper Case 

Information Unit Separator 

Vertical Tabulation 

Vertical Tabulation 

Wait Before Transmitting Positive Acknowledgement 

Who are you? 



34 



Prior to transmission of 
the letter B, the code LETS 
must be sent in order to set 
the receiving equipment into 
letter shift mode. The reason 
for this convention is to make 
it possible to transmit more 
than 32 symbols with five 
bits (g=5, b=2, a=32). After 
all, there are already 26 
uppercase letters and ten 
digits; then there is need for 
punctuation and special 
symbols, and function 
characters to control the 
printer. Once the operator 
intends to send a numeric 
character, the FIGS code is 
sent prior to the numeric 
string. In addition to the 
numeric characters, several 
other characters were sent in 
figures shift mode. Depending 
on the equipment used, 
various different graphics 
were assigned to the same bit 
strings. Table 3 indicates the 
assignments for four different 
keyboards; the first column 
shows the International 
Telegraph Alphabet No. 2 of 
the Comite Consultatif 
I nternational Telegraphique 
etTelephonique (CCITT); the 
second column shows the 
commercial teletype 
keyboard as used in the 
United States, the third 
column presents the fractions 
keyboard of the American 
Telephone and Telegraph 
Company (ATT); the fourth 
column shows the weather 
bureau keyboard. All four 
different keyboards are 
shown here because used 
equipment from different 
sources may be available to 
you which you might want to 
modify so that all keycaps 
correspond to the commercial 
keyboard. 

Binary Coded Decimal (BCD) 
Transmission Code 

The term "binary coded 
decimal" derives from the 
method of coding decimal 
digits. The bit string with 
value 9 is 1001, and the value 
10 is expressed by adding an 
additional four bits, namely, 
00010000. The bit string 



Table 3. Five-level Baudot Code for Four Selected Keyboards. 

Upper Case 
BIT 

CODE 1 













Lower E 
Case u 


ID 

E 
E 
o 
o 


< 


SI 
CO 

u 


1 


1 











A 


-- 


- 


- 


t 


1 








1 


1 


B 


? 


? 


5/8 


e 





1 


1 


1 





c 






1/8 


o 


1 








1 





D 


Who 
are you? $ 


$ 


/ 


1 














E 


3 


3 


3 


3 


1 





1 


1 





F 




! 


1/4 


— 





1 





1 


1 


G 




& 


& 


X 








1 





1 


H 




# 




I 





1 


1 








I 


8 


8 


8 


8 


1 


1 





1 





J 


Bell 


Bell 


• 


/ 


1 


1 


1 


1 





K 


( 


( 


1/2 


— 





1 








1 


L 


) 


) 


3/4 


\ 








1 


1 


1 


M 
















1 


1 





N 


, 


, 


7/8 


at 











1 


1 


O 


9 


9 


9 


9 





1 


1 





1 


P 














1 


1 


1 








Q 


1 


1 


1 


1 





1 





1 





R 


4 


4 


4 


4 


1 





1 








S 


, 


, 


Bell 


Bell 














1 


T 


5 


5 


5 


5 


1 


1 


1 








U 


7 


7 


7 


7 





1 


1 


1 


1 


V 


= 


; 


3/8 


0> 


1 


1 








1 


w 


2 


2 


2 


2 


1 





1 


1 


1 


X 


/ 


/ 


/ 


/ 


1 





1 





1 


Y 


6 


6 


6 


6 


1 











1 


z 


+ 


" 


" 


+ 



















Blank 




' 


- 


1 


1 


1 


1 


1 




Letters shift 




I 


1 


1 





1 


1 




Figures 


shift 




t 








1 










Space 






■ 











1 







Carriage 


return 




< 





1 













Line feed 




s 



35 



Table 4. Seven-bit American Standard Code for Information Interchange. 



Bits 
4 


3 


2 


Bits 7, 
1 


6, 5 


000 001 010 


011 


100 


101 


110 


111 


"^~\^Hex 
Hex 1~~^^^ 


1 2 


3 


4 


5 


6 


7 

















NUL 


DLE 


SP 





9 


P 


' 


P 











1 


1 


SOH 


DC1 


It! 


1 


A 


Q 


a 


q 








1 





2 


STX 


DC2 




2 


B 


R 


b 


r 








1 


1 


3 


ETX 


DC3 


ft 


3 


C 


S 


c 


s 





1 








4 


EOT 


DC4 


$ 


4 


D 


T 


d 


t 





1 





1 


5 


EIMQ 


NAK 


% 


5 


E 


U 


e 


u 





1 


1 





6 


ACK 


SYN 


& 


6 


F 


V 


f 


V 





1 


1 


1 


7 


BEL 


ETB 


■ 


7 


G 


w 


g 


w 


1 











8 


BS 


CAN 


( 


8 


H 


X 


h 


X 


1 








1 


9 


HT 


EM 


) 


9 


I 


Y 


i 


V 


1 





1 





A 


LF 


SUB 


* 




J 


z 


j 


z 


1 





1 


1 


B 


VT 


ESC 


+ 




K 


[ 


k 


i 


1 


1 








C 


FF 


FS 


, 


< 


L 


\ 


I 


i 
i 


1 


1 





1 


D 


CR 


GS 


- 


= 


M 


] 


m 


\ 


1 


1 


1 





E 


SO 


RS 




> 


N 


-l t A 


n 


~ 


1 


1 


1 


1 


F 


SI 


US 


/ 


? 










DEL 



tFor IBM 370, the left of the two symbols is generally displayed. See Table 2 for explanation of 
function abbreviations. 



TaWe 5. Six-bit Binary Coded Decimal Transmission Code. 



Bits 



Bits 3, 4 



-«^^ 1,2 


00 


01 


10 


11 


0000 


SOH 


& 


- 





0001 


A 


J 


/ 


1 


0010 


B 


K 


S 


2 


0011 


C 


L 


T 


3 


0100 


D 


M 


U 


4 


0101 


E 


N 


V 


5 


0110 


F 


O 


w 


6 


0111 


G 


P 


X 


7 


1000 


H 


Q 


Y 


8 


1001 


I 


R 


z 


9 


1010 


STX 


SPACE 


ESC 


SYN 


1011 




$ 


) 




1100 


< 


* 


% 


9 


1101 


BEL 


US 


ENQ 


NAK 


1110 


SUB 


EOT 


ETX 


EM 


1111 


ETB 


DLE 


HT 


DEL 



36 



01011001 therefore has a 
value of 59, and 99 is 
expressed as 10011001. This 
method differs from the bit 
coding shown in Table 1 . 

The binary coded decimal 
(BCD) transmission code has 
been widely used by IBM and 
other manufacturers to 
transmit uppercase letters, 
digits, and special symbols in 
a six-bit code. It is a subset of 
the USASCII code; however, 
it is not a national standard. 
The bit strings are shown in 
Table 5. 

The American Standard Code 
for Information Interchange 
(ASCII) 

Throughout the decades, 
many different data 
transmission codes were 
developed, and designers 
today often find good reasons 
to develop their own codes. 
The need for standardized 
transmission codes, however, 
has increased tremendously 
because more and more 
machines dial-up other 
machines via the public 
networks. The American 
Standards Association has 
standardized a seven bit code 
for communications. It 
contains upper and lower-case 
letters, and a large number of 
device and transmission 
control characters. An eighth 
bit may be added for parity. 
The term parity implies that 
the number of bits should 
add up to an even number 
(for even parity) or to an odd 
number for odd parity. The 
purpose is to check to some 
degree for a loss of bits 
during transmission. Assume 
that a device transmits in 



even parity; uppercase B 
consists of two marks and 
five spaces, therefore, no 
eighth bit is transmitted; 
uppercase T consists of three 
marks and four spaces, and an 
eighth mark is sent to make 
the number of marks even. 
Fig. 2 shows the string BYTE 
in even parity transmission. 
The code is shown in Table 4. 
Bit 1 is transmitted first. You 
may also want to refer to 
Table 2 in order to 
understand the meaning of 
the abbreviations. 

Extended Binary Coded 
Decimal Interchange Code 
(EBCDIC) 

The Extended Binary 
Coded Decimal Interchange 
Code is essentially the 
previously mentioned Binary 
Coded Decimal code 
extended by two bits to form 
an eight-bit code. A total of 
256 codes are possible (b=2, 
g=8, a=256) and because of 
its length of eight bits, it is 
often more easily expressed 
in hexadecimal notation by 
means of a string of two 
hexadecimal digits. Table 6 
shows both notations, the bit 
pattern and the hexadecimal 
notation. The digit 9, for 
example, is expressed as the 
bit string 11 11 1001, or as the 
hexadecimal string F9. 

The code is often used to 
transmit the eight-bit bytes of 
computers. It originated 
about a decade ago when IBM 
introduced the System 360. 
The terms "EBCDIC", 
"byte", and "hexadecimal 
digits 0, . . ., F" were 
developed at that time. 
Today these terms are widely 



accepted and used by many 
computer manufacturers. The 
code is also widely accepted; 
however, it is not a national 
standard. 



Conclusions 

A character is a unit of 
information which can be 
represented in various forms, 
such as in graphic form, or as 
a bit string. Since bit strings 
can be rather lengthy and 
therefore difficult to 
remember, we discussed the 
abbreviated representation of 
the string by means of the 
hexadecimal graphics. The 
relationship between the bit 
string representations of 
characters and the 
hexadecimal graphics is 
independent of the code since 
it is based on an intrinsic 
numerical order, namely that 
of counting from zero by one 
to infinity. 

On the other hand, bit 
strings may be represented by 
graphics in an entirely 
different manner depending 
on the code used. For that 
purpose we looked at the 
predominant five-, six-, seven- 
and eight-bit codes presently 
in use. We did not discuss 
various other but less 
important codes because of 
space limitations. Depending 
on the code utilized, the same 
graphic represents entirely 
different bit strings as shown 
in Table 7. 

The first character in the 
Baudot code is the letters 
shift. Note the similarity 
between the last three codes 
which holds only for 
uppercase letters and digits. 



Fig. 2. The word BYTE in Even-parity USASCII. 



MARKING 
"SPACING" 



^_^~^^^^^^^^^ 



<U 



Ho: I o 



ONE CHARACTER 



ONE CHARACTER 



ONE CHARACTER 



<h 



ONE CHARACTER- 



37 



Table 6. Eight-bit Extended Binary Coded Decimal Interchange Code. 



BitsO, 1 



Bits 2, 3 



Bits 

4. 5.6, 7 
0000 

0001 

0010 

0011 
0100 
0101 
0110 
0111 
1000 
1001 
1010 
1011 
1100 
1101 
1110 

1111 




00 



00 



01 



10 



11 



01 



00 



01 



10 



11 



10 



00 



01 



10 



11 



11 



00 



01 



10 



11 



NUL DLE DS SP 

SOH DC1 SOS 

STX DC2 FS SYN 

ETX TM 

PF RES BYP PN 

HT NL LF RS 

LC BS ETB UC 

DEL IL ESC EOT 

CAN 

EM 

SMM CC SM i 

VT CUT CU2 CU3 . 

FF IFS DC4 < 

CR IGS ENQ NAK ( 

50 IRS ACK + 

51 IUS BEL SUB I 



& — 



/ 



# 
% @> 

> 

? 



To conclude this tutorial, 
let me say this in EBCDIC 
(without start, stop and 
parity bits): 



D5 


85 


A7 


A3 


6B 


40 


A6 


85 


7D 


93 


93 


40 


84 


89 


A2 


83 


A4 


A2 


A2 


40 


95 


A4 


94 


82 


85 


99 


A2 


4B 







A 
B 
C 
D 

E 
F 
G 
H 
I 



J 

K 

L 

M 

N 

O 

P 

Q 

R 



S 

T 
U 
V 

w 

X 
Y 

z 



r 



Special Graphic Characters 



1 



i 
< 



Cent Sign 

Period, Decimal Point 

Less-than Sign 

Left Parenthesis 

Plus Sign 

Logical OR 

Ampersand 

Exclamation Point 

Dollar Sign 

Asterisk 

Right Parenthesis 

Semicolon 

Logical NOT 



Minus Sign, Hyphen 

Slash 

Comma 

Percent 

Underscore, Break 
Character 



> 

? 



L_ 



Greater-than Sign 
Question Mark 
Colon 

Number Sign 
At Sign 

Prime, Apostrophe 
Equal Sign 
Quotation Mark 
See Table 2 for explanation of function abbreviations. 



# 
@ 



J 



Table 7. Transmission of the String BYTE in selected codes (excluding 
start, stop) and parity bits). 



11111 10011 10101 00001 10000 

000010 101000 100011 000101 
0100001 1001101 0010101 1010001 
11000010 11101000 11100011 11000101 



Baudot 

BCD Transmission Code 

USASCII (see Note 1) 

EBCDIC 



Note 1. In memory, the sequence of bits on the IBM 360 and 370 is 
reversed. The left bit shown becomes the right bit, etc., as shown: 

1000010 1011001 1010100 1000101 



38 



featuring MITS Altair Computers 

FULL SERVICE COMPUTER STORE 

Byte'Tronics is the hobbyist's dream come true. A full service computer store featuring 
the full line of Altair Computer products backed by the most complete technical seivice 
available. 

The prices at Byte'Tronics are MITS factory prices and most items are available on 
an off-the-shelf basis. 

Byte'Tronics sponsors the local Altair Users Group of East Tennessee and Byte'Tronics is 
interested in communicating with computer hobbyists throughout the world. 

If you have a question about Altair hardware (whether or not you are a Byte'Tronics 

customer), we will put you directly in touch with our Technical Director, Hugh Huddelston. Hugh 
is an expert troubleshooter who has a thorough knowledge of each portion of each Altair 
board. And he can answer all your questions about custom interfacing. 

If you have questions about software or if you want some custom programming, our 
Software Director, Johnny Reed, is the expert who can take cere of your needs. Johnny has 
had years of programming experience, and he is familiar with Altair BASIC, assembler and 
machine language programming. 

If you have questions about the availability of a MITS product or its price or specifications, 
we will let you talk to Bruce Seals, our Director of Marketing. 

At Byte'Tronics we want you to understand your Altair and we are willing to give you all 
the technical support you need. 

Byte'Tronics sells computers. Byte'Tronics sells service. 

For more information, visit our store in Knoxville— or write or call us. We want to hear 
from you. 





5604 Kingston Pike, Knoxville, Tennessee 37919 Phone 615-588-8971 
Office hours: 10 a.m. to 10 p.m. Monday-Friday and 9 a.m. to 10 p.m. Saturday. 





MITS-MAS 




Christmas Catalog 



Lowest Price in the World! 




In January of 1975. MITS stunned the computer world with 
the announcement of the Altair 8800 Computer that sells for 
$439 in kit form. 

Today MITS is announcing the Altair 680. 

The Altair 680. built around the revolutionary new 6800 
microprocessor chip, is the lowest priced complete computer on 
the market. Until December 31, 1975, this computer will be sold 
in kit form for the amazing introductory price of $293! (A 
savings of $52!) 

The Altair 680 comes with power 
supply, front panel control board, 
and CPU board inclosed in an 
11" wide x 1 1" deep x 4 1 1/16" case. 
In addition to the 6800 processor, 
the CPU board contains the following 

1. 1024 words of memory (RAM 
2102 type 1024 x 1-bit chips). 

2. Built-in Interface that can 
be configured for 
RS232or20mA 
Teletype loop 
or 60 mA 
Teletype. 

3. Provisions for 
1024 words of 
ROM or PROM. 

The Altair 680 can be 
programmed from the front 
panel switches or it can be 

connected to a computer terminal (RS232) or a Teletype such as 
an ASR-33 or surplus five-level Baudott Teletype (under $100). 

The Altair 680 can be utilized for many home, commercial or 
industrial applications or it can be used as a development system 
for Altair 680 CPU boards. With a cycle time of 4 microseconds, 
16-bit addressing, and the capability of directly addressing 
65,000 words of memory and a virtually unlimited number of 
I/O devices, the Altair 680 is a very versatile computer! 

Altair 680 Software 

Software for the Altair 680 includes a monitor on PROM, 
assembler, debug, and editor. This software is available to Altair 
680 owners at a nominal cost. 

Future software development will be influenced by customer 
demand and may include BASIC on ROM. MITS will sponsor 
lucrative software contests to encourage the rapid growth of the 
Altair 680 software library. Programs in this library will be made 
available to all Altair 680 owners at the cost of printing and 
mailing. 

Contact factory for updated information and prices. 

Altair Users Group 

All Altair 680 purchasers will receive a free one year 
membership to the Altair Users Group. This group is the largest 
of its kind in the world and includes thousands of Altair 8800 and 
680 users. 

Members of the Altair Users Group are kept abreast of Altair 
developments through the monthly publication, Computer 
Notes. 



Altair 680 Documentation 

The Altair 680 kit comes with complete documentation 
including assembly manual, assembly hints manual, operation 
manual, and theory manual. Assembled units come with 
operation and theory manuals. Turnkey model and CPU boards 
also include documentation. 

NOTE: Altair 680 manuals can be purchased separately. 
See backpage of this catalog for prices. 

Delivery 

Personal checks take 2-3 weeks to 

process while money 
orders and credit card 
purchases can be 
processed in 1-3 days. 
Delivery should be 
30-60 days but this 
can vary according to 
order backlog. All 
orders are handled 
on a first come, first 
served basis. 

Altair 680 Prices 

Altair 680 complete computer kit .... $293 
($345 after December 31, 1975) 

Altair 680 assembled and tested $420 

Altair 680T turnkey model (complete Altair 680 except 

front panel control board) Kit Only $240 

($280 after December 31, 1975) 
Altair 680 CPU board (including pc board, 6800 micro- 
processor chip, 1024 word memory, 3 way interface 

and all remaining components except 

power supply) $180 

($195 after December 31, 1975) 

Altair 680 CPU board assembled and tested $275 

Option I/O socket kit (required when interfacing 

680 to external devices) $ 29 

Option cooling fan (required when expanding 

680 internally) $16 

($22 after December 31, 1975) 

Option cooling fan installed $ 26 

PROM kit (256 x 8-bit ultraviolet, erasable 

1702 devices) $42 




\mw\} 




"Creative Electronics 

Prices, delivery and specifications subject lo change. 



"PROJECT BREAKTHROUGH! 

World's First Minicomputer Kit 
To Rival Commercial Models . . 
'Altair 8800' " 



The Altair 8800 from MITS is now one of the most 
successful computers ever delivered. Thousands of Altair 
8800s have been sold and are in the field where they are 
being used for an infinite variety of industrial, business, 
science and home applications. 

The Altair 8800 is extensively supported 

by ongoing hardware and 

software development. 

Altair 8800 interface and 

memory modules and 

Altair peripherals are 

inexpensively priced, yet 

among the highest quality 

in the business. Byte for 

byte, Altair 8800 BASIC 

language software is the 

most powerful BASIC 

ever written. 

Thanks to the success of the 

Altair 8800, building and 

programming computers has 

become one of the World's most exciting 

and fastest growing hobbies. Local Altair 8800 

Users Clubs have been formed across the United 

States and in such far away places as England and Japan. 

Thanks to clean, efficient design and accurate, easy to 
understand assembly instructions, the Altair 8800 is an 
easy kit to assemble. As an Altair 8800 kit builder, you will 
have the satisfaction of successfully building your own 
computer and you will learn about the internal structure of 
digital computers. 

As the owner of an Altair 8800, you will be backed by the 
technical expertise of the MITS Customer Service 
Department. You will receive the latest update 
information, programming hints, technical advice and 
general computer information on a monthly basis through 
a free subscription to Computer Notes. You will be in 
contact with other Altair 8800 owners through the Altair 
Users Group and you will have access to the extensive 
Altair 8800 Software Library. 

No other computer on today's market can offer you 
as much support as the Altair 8800. 

Christmas Special 

For a limited time only, you can be the owner of an Altair 
8800 with a 1,024 word memory module for just $68 a 
month! See back page of this catalog for all the details. 




headline on cover of Popular Electronics, 
January, 1975 

Altair 8800 Features 

Built around the most successful (and many say the most 

powerful) microprocessor 
chip ever [the Intel 8080] , the 
Altair 8800 is a variable word 
length computer with an 8-bit 
processor, 16-bit addressing 
and a maximum word size 
of 24-bits. It has 78 basic 
machine instructions with 
variances over 200 instructions. 
The Altair 8800 can directly 
address 256 input and 256 
output devices and up to 
65,000 words of memory. 

Up to 300 peripherals can be 
interfaced to the Altair 8800 
without any additional buffering. 
The custom designer can interface 
almost any number of imaginable devices 
simultaneously. All Altair peripherals are 
supplied with software handlers to make 
interfacing easy. 

The Altair 8800 includes the CPU board, front 

panel control board, power supply (enough to power any 

additional cards), and expander board (with room for 3 

extra interface or memory modules) all inclosed in a 

handsome, aluminum case complete with sub-panel and 

dress panel. Up to 16 cards can be added inside the main 

case. 



Altair 8800 Prices 

Altair 8800 Computer kit (includes 
assembly hints, assembly, operator's, 
and theory manuals) $439 

Altair 8800 assembled $621 

Expander board (adds 4 slots) $ 16 kit 

assembled, $ 31 

Cooling fan $ 16 kit 

assembled, $ 20 



Altair Modules — 

Custom Design Your Computer System to Meet Your 
Application (and stay within your budget!) 








■ssf 




1. Three 8800 memory modules. Three 

memory modules are now available for the 
Altair 8800 and more are in the works. These 
modules include a IK (1,024) word static card, 
a 2K (2,048) word static card, and a 4K (4,096) 
word dynamic card. Each of these modules is 
constructed with the finest components 
available and each contains memory protect 
features (prevents the computer from accidently 
writing over programs you want to save). The 
maximum access time of the static cards is 850 
nanoseconds while access time for the dynamic 
card is 300 nanoseconds. 

2. Four 8800 Interface Modules. Interface 
modules now available for the Altair 8800 in- 
clude three serial and one parallell I/O cards. 
The SlOA serial card is used to connect the 
Altair 8800 to CRT's and other computer ter- 
minals that have industry standard RS232 
asynchronous interconnect lines. It has divider 
logic to allow for presettable baud rates up to 
19.200 baud (5-8 data bits). 

The SIOB is the same as the SIOA except that 
all signals are TTL levels. This card is a general 
purpose serial interface that can be used to 
custom interface the Altair 8800 to a wide varie- 
ty of devices. 

The SIOC is also the same as the other serial 
cards except it is used to interface the Altair 
8800to conventional Teletypes and other asyn- 
chronous 20 mA current loop terminals. The 
SIOC is required to interface the Altair with 
ASR-33 Teletypes available from MITS. 

The PIO parallel interface card is used for 
bidirectional transmission of bytes at speeds up 
to 25,000 bytes/second! It is a full TTL compati- 
ble input/output card with necessary hand- 



shake flags for conventional parallel interface. 
Both input and output data have their own 8-bit 
latch for buffering. Includes necessary logic to 
allow an adjacent channel to be a control 
channel. Most commonly used to interface the 
Altair 8800 to SWTPC-TVTs or equivalent, 
custom A/D-D/ A interfacing, computer to com- 
puter interfacing, and control applications. 

3. Audio-Cassette Interface. This best- 
selling A/tairmodule allows you to connect your 
Altair 8800 to any tape recorder (medium quali- 
ty cassette is adequate) for inexpensive mass 
storage. It works by modulating (changing) 
digital signals from the computer to audio 
signals for recording data and by demodulating 
the audio signal for playback. Consists of a 
special Altair modem board "piggy-backed" on 
an SIOB board. Requires one slot in the 8800. 

4. 8800 PROM module. This PROM 
memory card is designed to hold up to 2K of 
PROM. Contact factory for price and other in- 
formation. Altair 8800 PROM Programmer to 
be announced soon. 

5. 680 CPU board. The Altair 6S0CPU board 

is a complete computer on a board (less power 
supply). In addition to the 6800 CPU available 
from Motorola and AMI, the Altair 680 CPU 
board comes with IK of RAM memory (2102 
type, 1024 x 1-bit chips), built-in I/O that can be 
configured for RS232 or 20 mA current loop or 
60 mA current loop, and provisions for IK of 
ROM or PROM. It measures 8 V x 10%". 

6. 8800 CPU board. The heart of the Altair 

8800 is its CPU board. This double-sided board 
was designed around the powerful byte 



oriented, variable word length 8080 pro- 
cessor — a complete central processing unit on a 
single LSI chip using n-channel, silicon gate 
MOS technology. The CPU board also contains 
the Altair system clock — a standard TTL os- 
cillator with a 2.000 MHz crystal as the feedback 
element. 

Altair Module Prices: 

IK static memory $97 kit 

and $139 assembled 

2K static memory $145 kil 

and $195 assembled 

4K dynamic memory $195 kit 

and $275 assembled 

SIOA interface $1 19 kit 

and $138 assembled 

SIOB and SIOC interface $124 kit 

and $146 assembled 

PlOinterface $92kit 

and $114 assembled 

Audio-cassette interface $128 kit 

and $174 assembled 

680 CPU board kit $180kit 

[$195 after December 31, 1975] 

680 CPU board, assembled $275 

8800 CPU board $310kit 

and $360 assembled 

NOTE: Watch our advertisements 
for announcement of new Altair 
8800 modules and Altair 680 
modules. 



BASIC language was chosen for the Altair 8800 because it is the easiest 
language to learn and because it can be used for an infinite number of 
applications. Literally hundreds of thousands of BASIC programs have 
been written and are in the public domain. These programs include ac- 
counting programs, business programs, scientific programs, educational 
programs, game programs, engineering programs, and much more. 

Altair BASIC is an interactiue language. This means that you get im- 
mediate answers and you can use your Altair as a super programmable 
calculator as well as for writing complicated programs. 



8K BASIC Features 

Altair 8K BASIC leaves approximately 2K bytes in an 8K Altair for 
programming which can also be increased by deleting the math functions. 
This BASIC is the same as the 4K BASIC only with 4 additional 
statements [ON GOTO, ON . . . GOSUB, OUT. DEF], 1 ad- 
ditional command [CONT] and 8 additional functions [COS, LOG, 
EXP, TAN, ATN, INP, FRE, POS]. Other additional features include multi- 
dimensioned arrays for both strings and numbers, AND. OR. NOT 



hh I've seen and used other BASICs, but byte-for-byte, Altair 
is the most powerful BASIC I've seen. I'm particularly im- 
pressed with the n-dimensional arrays (and for strings 
too!), machine level I/O, and machine language Junction 
features. The level of your documentation is, for me, 
though the high point. Sections for those who know 
nothing and sections for those who know a lot, plus sec- 
tions that 'normal' people can read and understand. ^ 

J. Scott Williams 
Bellingham, Washington 

Altair BASIC was written as efficiently as possible to allow for the max- 
imum number of features in the minimum amount of memory. You can 
order one of three Altair BASICs: 4K BASIC-designed to run in an Altair 
8800 with as little as 4K of memory, 8K BASIC, or EXTENDED BASIC 
(12K). Each of these BASICs allows you to have multiple statements per 
line (a memory saving feature), and each of them is capable of executing 
700 floating point additions per second! 



The 8K BASIC and EXTENDED BASIC have multi-dimensioned 
arrays lor both strings and numbers. This is particularly useful for 
applications requiring lists of names or numbers such as accounting 
programs, inventory programs, mailing lists, etc. 

The 8K BASIC and EXTENDED BASIC also have an OUT and cor- 
responding INP statement that allows you to use your Altair 8800 control 
low speed deuices such as drill presses, lathes, stepping motors, model 
trains, model airplanes, alarms, heating systems, home entertainment 
systems, etc. 

Altair BASIC comes with complete documentation including a copy of 
"My Computer Likes Me When I Speak in BASIC" by Bob Albrecht, a 
beginner's BASIC text. 

Never before has such a powerful BASIC language been 
marketed at such low prices! 



4K BASIC Features 

Altair 4K BASIC leaves apporimxately 750 bytes in a 4K Altair for 
programming which can be increased by deleting the math functions. This 
powerful BASIC has 16 statements [IF THEN, GOTO, GOSUB, 
RETURN, FOR, NEXT, READ, INPUT, END, DATA, LET, DIM, REM, 
RESTOR, PRINT, and STOP] in addition to 4 commands [LIST, RUN, 
CLEAR. SCRATCH] and 6 functions [RND, SQR, SIN, ABS, INT and 
SGN]. Other features include: direct execution of any statement except 
INPUT; an'V' symbol that deletes a whole line and a "-<- "that deletes 
the last character; two- character error code and line number printed when 
error occurs; Control C which is used to interrupt a program: maximum 
line number of 65.535: and all results calculated to at least six 
decimal digits of precision. 



operators that can be used in IF statements or forumlas, strings with a 
maximum length of 255 characters, string concatenation (A$ = B$) and 
the following string functions: LEN, ASC CHAR$. RIGHT$. LEFT$, 
M1D$. STR$. and VAL. 

EXTENDED BASIC 

Altair EXTENDED BASIC is the same as 8K BASIC with the addition 
of double precision arithmetic. PRINT USING and disk file I/O. A 
minimum of 12K memory is required to support EXTENDED BASIC. 

Other Altair 8800 software includes a Disk Operating System, 
assembler, text editor, and system monitor. Altair users also have access to 
the Altair Library, which contains a large number of useful programs. 



SOFTWARE PRICES: 

AItair4K BASIC $150 

Purchasers of an Altair 8800, 4K of Altair memory, 

and an Altair I/O board $ 60 

Altair 8K BASIC $200 

Purchasers of an Altair 8800, 8K of Altair memory, 

and an Altair I/O board $ 75 

Altair Extended BASIC $350 

Purchasers of an Altair 8800, 12K of Altair memory, 

and an Altair I/O Board $150 

Altair PACKAGE ONE (assembler, text editor, 

system monitor) $ 175 

Purchasers of an Altair 8800, 8K of Altair memory, 

and an Altair I/O board $ 30 

Altair Disk Operating System $500 

Purchasers of an Altair 8800, 12K of Altair memory, 

Altair I/O and Altair Floppy Disk $150 

Note: When ordering software, specify paper tape or 
cassette tape. 



Inexpensive, Sophisticated Mass 
Storage 

converts serial data to 8-bit parallel words and vice versa for rapid 
transfer. 

The disk drive consists of a Pertec FD400 drive mounted in an 
Altair case including power supply, a buff/multiplexer board, and 
cooling fan. Its rotational speed is 360 rpm, track to track access 
time is 10 msec, average time to read or write is 400 msec, and 
disk life is over 1 million passes per track. 

The floppy disk is hard sectored for 32 sectors per track (128 
words per sector). There are 77 tracks on each disk. Extra floppy 
disks are available for $15 from MITS. 

A Disk Operating System (software) with complete file struc- 
ture and utilities for copying, deleting and sorting files is also 
available. 

PRICES: 

88-DCDD Altair Disk (includes 

The Altair Disk can store over 300,000 words of information disk controller, disk drive, one floppy disk 

on a floppy disk! It offers the advantage of nonvolatile memory and software driver) $1,480 kit 

(doesn't "forget" when power is turned off) and fast access to assembled, $1,980 

data ( 94 seconds— worst case ) . The data transfer rate of the Altair 88-DISK Altair Disk Drive only $ 1 , 180 kit 

Disk to and from the computer is a whopping 250,000 bits per assembled, $1,600 

second. Floppy disk $ 15 

The Altair Disk includes the disk controller, disk drive, one Disk Operating System 

floppy disk and a software driver. The disk controller, which con- (if purchased separately) $ 500 

sists of two cards requiring two slots in the 8800. is capable of Purchasers of an Altair 8800, 12Kof 

controlling up to 16 disk drives. It controls all mechanical func- Altair memory, Altair I/O and 

tions of the disk, presents the disk status to the computer, and Altair Disk (88-DCDD) $ 150 




Build Your Own Advanced 
Terminal! 




The Comter 11 is easily the most advanced computer terminal 
kit on the market. It has its own internal memory of 256 
characters which combines with a highly-readable, soft orange 32 
character display to provide ease of operation and information 
retrieval. 



Complete cursor control allows you to move data in and out 
of the display and operate the Comter II with the versatility of a 
CRT terminal. Built-in audio-cassette interface allows you 
to store unlimited data from the computer and feed that 
information back into the computer. 

Other features include auto transmit which allows line-by-line 
transmission of data or program information to the computer 
from the Comter's memory. The Comter II has a complete ASCII 
encoded keyboard with TTY-33 format plus the addition of 
special function keys. Its total weight is just 15 lbs. 

Flexible power requirements allow you to operate the com- 
puter at either 95-125V or 190-250V. The Comter II can be inter- 
faced to any computer with an RS232 serial interface. Requires 
an SIOA board to be connected to the Altair 8800. No interface 
required to connect to the Altair 680. 

PRICES: 

Comter II kit with built-in 

audio cassette I/O $780 

Comter II assembled $920 



High Speed Printing at Low Cost! 



The Altair 110 Line Printer is a desktop line printer that 
produces 80 columns of 5 x 7 dot matrix characters at 100 
characters per second x 70 lines per minute. The impact head 
prints bidirectionally on a 8V2" roll paper* using a conventional 
teletype ribbon. The Altair Line Printerwill print up to four copies 
of any item. 

Maximum reliability is provided by a mechanism which con- 
tains no brakes, clutches, dampers or stepper motors. All control 
electronics including one-line buffer and self-test circuitry are 
contained on a single 5" x 15" printed circuit card. The Model 
110 was expressly designed for the simplicity, reliability and ex- 
tremely low cost required by current small-scale data handling 
systems and terminals. 

Vibration and wear are minimized because the print head 
moves uniformly in both directions and pauses only at the end of 
each line. Opto-electronic sensing is used to accurately position 
each dot and permit characters to be printed on the fly. 

The Altair 110 Line Printer comes with complete control elec- 
tronics including a printer control card. Requires one slot in the 
Altair 8800. 

* Pin-fed Optional. 




PRICES: 

Altair Line Printer with 
controller card 



$1,750 kit 

assembled, $1,975 



Very Low Cost 
Terminal 



Teletype — 
Most Versatile 




The Altair VLCTis ideal for machine language programming. 
It converts a three digit octal code directly into an 8 digit binary 
code for transmission to the computer and then displays the 
binary output from the computer in a 3 digital octal format. This 
allows you to program in octal which is much easier than 
programming in binary. In addition, the VLCT is much more con- 
venient to work with than using the front panel switches of the 
Altair 8800. 

PRICES: 

VLCT $129 kit 

assembled, $169 

NOTE: PIO interface module is required to connect 
VLCT to Altair 8800. 




With a built-in paper tape reader and punch and hard copy 
output, this ASR-33 Teletype is perhaps the most versatile of all 
low cost input/output devices. 

The ASR-33 Teletype prints 10 characters per second. It is a 
completely checked-out machine with standard 120 day warran- 
ty. 

PRICE: 

ASR-33 Teletype $1,500 

NOTE: SIOC interface module is required to connect 
Teletype to Altair 8800. 



Christmas Time Payment Plan Altair Manuals 

IK Altair for Just $68 a Month! Jff «£? ? perat ° rs $ 7 - 50 

^ Altair 8800 Assembly $ 9.00 

You can be the owner of an Altair 8800 with a 1.024 Altair 8800 Theory, Schematics $10.00 

word memory module for just $68 a month. Eacli month Altair 680 Operators $ 7.50 

it o ii \ j • 1 1 Altair 680 Assembly $ 7 50 

tor a months you send in your payment and we send A1 _ . ,„„ T , c . . * 

, A u . 1 ., \., , , Altair 68 <> Theory, Schematics $10.00 

you part of an Altair kit until you have the complete BASIC Language Documentation $10.00 

system. The advantages of the plan are NO interest or Assembler. Monitor, Editor $ 7.50 

financing charge, GUARANTEED price based on today's 88 00 4K Memory (includes Assembly.Theory & Schematics) . $ 5.00 

price, and free, immediate membership to the Altair Users 88()0 2K Memor y $ 5.00 

Group including subscription to Computer Notes. 5?™ I™emory f 5t)0 

00OO blOA $ 5.00 

Our terms are cash with order, BankAmericard, or Master 8800 SIOB $ 5.00 

Charge. If you send in an early payment, we will make 8800 SIOC $ 5.00 

an early shipment. By the same token, a late payment 880() P1 ° $ 5 - 00 

will result in a late shipment. (After 60 days past due, mmra „'„ * *!'?? 

.. , 1 1 ., , . 11 . a 11 _ COM rhR " Operators $ 6.50 

the balance ot the deal is cancelled. All payments must COMTER II Assembly $10 00 

be made within 10 months). COMTER II Theory, Schematics $10.00 

Total $544.00 (Retail price: Altair 8800 $439.00, Memory VLCT (Assembly, Operators, Theory) $ 5.00 

$97.00. Postage and Handling $8.00- Alu,ir Line Printer Interface $ 5.00 

total $544.00) 

Documentation Special One 

Altair USerS GrOUp Special Altair 8800 Operators. Assembly and Theory manuals plus BASIC 

Each month the Altair Users Group sponsors a software contest and Language manual (regularly $36.50). Now just $15.00. 
each month MITS gives away $130 in credit to the winners of this 
contest. At the end of the year, the author of the overall best program DoCllIllCFltcltioil S|> CC_ciI TwO 

will receive $1000 in credit. ,. . , ,„. „ . , . . _. , _ , , .__. 

Altair oho Operators. Assembly and Iheory manuals. Regularly $25. 
Membership to the Altair Users Group (the largest of its kind in the Now jusl $14 50 

world) is free to Altair 8800 owners. However, even if you don't own an 

Altair. you can be an associate member for one year 'at the special ,ow Documentation Special Three 

pnee of $10 (regularly $30). * 

As a member of the Altair Users Group, you will be kept informed of BASIC Language manual. Package I (Assembler. Monitor. Editor), and 

Altair developments, software contests, and general computer news BASIC, language beginners text (My Computer Likes Me When I Speak 

through the monthly publication. Computer Notes. You will have access BASIC by Bob Albrecht). Regularly $l c ).50. Now just $12.50. 
to the Altair Software Library and you can communicate to other Altair 

users throughout the world. MITS/6328 Linn NE/ Albuquerque, NM 87108 

Note: These specials expire on January 30. 1976. 505-265-7553 or 262-1951 

Mail this special Altair Coupon Today! 

□ Enclosed is check for $ □ BankAmericard # □ or Master Charge # 

□ Altair 8800 □ Kit □ Assembled □ Fan □ Christmas Time Plan □ Expander Board 

□ Altair 680 □ Kit □ Assembled □ Fan □ I/O Sockets 

D Teletype □ Line Printer □ Comter II □ VLCT □ Disk □ Disk Drive Only □ Disk Controller Only 

□ Memory Module □ I/O Module list »n sepvmm- sHeet) 

Postage & Handling: Add $8 for Altair 8800 or Altair freight. Warranty: 90 days on parts for kits and 90 
680 and $3 for any cards or peripherals if ordered days on parts and labor for assembled units. Prices, 
separately. Teletype and Line Printer shipped by collect specifications, and delivery subject to change. 

□ Documentation Special One □ Documentation Special Two □ Documentation Special Three 

□ Altair Users Group plus Computer Notes 

□ Please put me on your mailing list SHIP TO: 

BILLTO: MA*,* 

NAME : 

NAME : 

ADDRESS 

ADDRESS 

CITY 

CITY 

STATE & ZIP ; 

STATE & ZIP _ 

□ Please send Christmas Card to above address 

COMPANY (IF APPLICABLE) announcing gift and anticipated delivery. 

MITS/6328 Linn NE/Albuquerque, NM 87108 505-265-7553 or 262-1951 



LIFE Line 3 



by 

Carl Helmers 
Editor, BYTE 



Program design is a process which can be approached in a 
haphazard manner - or by a systematic exploration of what is 
needed to achieve the desired end. LIFE Line 2 in BYTE #2 
began the systematic exploration of the Tree of LIFE by 
presenting information on the overall program design of LIFE, 
as well as the details of the GENERATION algorithm used to 
carry one generation of LIFE into the next. 

LIFE Line 3 continues the development of LIFE by a 
discussion of the KEYBOARD INTERPRETER procedure. 
This procedure monitors the "user inputs" of a keyboard, and 
uses the command keystrokes detected to dictate what LIFE 
will do. As in the exploration of the GENERATION 
algorithm, the presentation starts at the top and works 
downward. 



Fig. 1. Data concepts for LIFE program and graphics control. The 
variables XCOL, YROW, N and ENTRY are 8-bit "software registers" 
maintained as variables in the LIFE program. 



DISPLAY SCREEN IMAGE 



INCREMENT/ DECREMENT 
INPUTS FROM MOVECURS 
ROUTINE 



DEFAULT N= AT START 

OF KEYBOARD INTERPRETER 



Y CURSOR 
POSITION 



-Y" COMMAND 



GENERATION COUNT 



— N"COMMAND 




NCREMENT/DECREMENT X 
INPUTS FROM MOVECURS 
ROUTINE 



X"COMMAND 



ENTRY 
REGISTER 



DEFAULT ROUTINE ASCII NUMERIC- 
DATA DEFINES ENTRY 




SPECIAL LIFE CONTROL 
PANEL AND ASCII 
KEYBOARD 



Much of the challenge and 
fun of the LIFE application is 
the fact that it is best 
implemented with some form 
of interactive graphics. In the 
partition of the application 
presented in LIFE Line 2, 
one of the major pieces of the 
program is the KEYBOARD 
.INTERPRETER with its 
interactive graphics concepts. 
A good place to start the 
discussion of the 
KE YBOA RD.INTER- 
PRETER is the software 
block diagram of the 
interactive graphics system of 
LIFE. 

A Software Block Diagram? 

Yes! Strange as it may 
sound to hardware types, the 
ebb and flow of data in a 
program can be depicted in 
block diagrams. While Fig. 1 
looks very much like an 
ordinary hardware block 
diagram of some system, it is 
descriptive of the plan of data 
flow in a program rather than 
actual wires. Fig. 1 is the 
programming equivalent in 
every respect of the hardware 
block diagram of some 
dedicated interactive graphics 
system. By retaining the 
system in software, LIFE is 
inherently more flexible than 
any hard-wired system could 
be. This block diagram 
illustrates the potential flow 
of data in LIFE as controlled 
through the KEYBOARD. 
INTERPRETER and its 



48 



Fig. 2. An overall view of the KEYBOARD_INTERPRETER. This is a 
flow chart of the control algorithm for the LIFE application's 
KEYBOARD_INTERPRETER routine. Fig. 3 shows the same informa- 
tion in the form of a procedure-oriented language. 



(KEYBOARD A 
INTERPRETER J 



subroutines. Data flows and 
changes in response to the 
several input commands 
defined for the program. 

As was pointed out in 
LIFE Line 1 , the 
fundamental tool of an 
interactive graphics 
application is a cursor which 
illustrates where the program 
thinks attention should be 
placed. This cursor is flashed 
on and off on the screen, and 
can be moved through 
appropriate commands of the 
user sent via a keyboard. The 
cursor concept is 
implemented in the LIFE 
program application by 
means of two "global" 
variables called XCOL and 
YROW. These are both 8-bit 
bytes of data. But since the 
maximum dimension value in 
either the X or Y directions 
of the display is 63 (i.e., 6 
bits) only the low order 6 bits 
have significance for cursor 
control. At any point in time 
during the execution of 
LIFE, the variables YROW 
and XCOL retain the location 
of the cursor for 
KEYBOARD_INTER- 
PRETER'suse. 

Fig. 1 also shows arrows 
directed from XCOL and 
YROW to intersecting dotted 
lines in the LIFEBITS array. 
These two numbers together 
have 12 bits of significance. 
This is sufficient to uniquely 
specify one of the 4096 bits 
in the array using the utility 



subroutines LGET and LPUT 
to reference and change 
LIFEBITS, respectively. 
These routines are left to a 
later LIFE Line for their 
details. 

A "ghost copy" of 
LIFEBITS is also shown in 
back of the main copy in the 
drawing to emphasize the 
following point: Each bit of 
the internal LIFEBITS array 
maps directly into a 
corresponding bit in the 
refresh memory of the CRT 
display subsystem. This is an 
example of a common theme 
throughout the use and abuse 
of computer systems: 
Software systems map into 
corresponding hardware — 
and vice versa. This mapping 
is of course one to one, and is 
carried out by the DISPLAY 
subroutine whenever the 
internal data is changed. As 
with LGET and LPUT, 
DISPLAY is left to a future 
LIFE Line for its details. 

What Does it Take to Move 
the Cursor? 

Since the cursor position is 
maintained by the values of 
XCOL and YROW, the 
movement of the cursor is 
simplicity at its essence: To 
move the cursor, all you have 
to do is change the value of 
XCOL, YROW or both! The 
interactive graphics portion 
of KEYBOARD_INTER- 
PRETER has as its primary 
concern the various ways of 



OLDKEY - NULL 
GO= FALSE 



5. DO UNTIL 




6. DO WHILE **- 



OLDKEY -NULL 



TIMEOUT = 
LONGTIMEWAIT 




READ 
KEYBOARD 



CALL 
DECODE 



CALL 

REPEATWAIT 

(TIMEOUT) 




)--' 



CALL 
CURBLINK 



I 



Loop actively blinks 
the cursor while waiting 
3r non-null key code . . . 
This branch is not taken 
n case of repeated key.) 





YES 




TIMEOUT = 


:Y ^S~ 






SHORTIMEWAIT 


NO 







Time out between 

repeated operations starts 

ttfl equal to LONGTIMEWAIT. 

set to SHORTIMEWAIT after 

the second time delay . 



49 



The simultaneous advantage 
and disadvantage of the 
multiple conditional test 
method of decoding: It 
is a plodding (but straight- 
forward) approach which 
squanders memory resources. 



changing the values of these 
two crucial variables — while 
possibly leaving a trail of 
changed data points in 
LIFEBITS. Fig. 1 illustrates 
several of these changes — 

— To move the cursor up, 
YROW is incremented. 

— To move the cursor 
down, YROW is 
decremented. 

— To move the cursor left, 
XCOL is decremented. 

— To move the cursor right, 
XCOL is incremented. 

— To completely redefine 
the column of the cursor, 
the ENTRY register is 
transferred to XCOL. 

— To completely redefine 
the row of the cursor, the 
ENTRY register is 
transferred to YROW. 

KEYBOARD_INTER- 
PRETER performs these 



actions at the whim of the 
user via commands entered at 
the keyboards of the system 
- with the flashing cursor 
mark on the screen showing 
the results. 

The ENTRY Register 

In order to provide a 
means of entering 8-bit 
integers into the program for 
control purposes, the 
software of KEYBOARD„ 
INTERPRETER maintains a 
numeric input area called 
ENTRY. Whenever an ASCII 
character is sent to the 
program which cannot be 
decoded by DECODE's 
COMMAND table, the last 
resort is to call DEFAULT. In 
DEFAULT, the recover 
assumption is to interpret the 
unknown command as a 
numeric digit (0 to 9) and 
push it into ENTRY. A 
routine in DEFAULT 
performs a BCD to binary 
conversion of the ASCII 
character after it has been 
trimmed to the range to 9. 
Later, when the user wants to 
define XCOL, YROW or N, 
the commands X, Y and N 
respectively are used to 
transfer ENTRY to one of 
the other registers, after 
which ENTRY is set to in 
preparation for re-use. It is 
important to emphasize that 
ENTRY is a binary number. 
When decimal digits are 
entered by the user, the input 
routines convert the digits 
into the appropriate binary 
number and decimally shift 
the significance of the 
previous value. 

The N Register 

In LIFE Line 2, the LIFE 
program given in Fig. 3 
references a variable called N. 
This N is used to control the 
number of times 
GENERATION is called. N, 
like XCOL and YROW, is a 
"software register" in the 
LIFE program which may be 
set by a user command. The 
"N" command is what is used 
to transfer the ENTRY value 
to N for use in controlling the 



Fig. 3. The KEYBOARDJN TERPRETER routine's overall flow, 
expressed in a procedure-oriented language. Note that the interpreta- 
tion of the "DO WHILE" differs from a "DO UNTIL" - the former has 
its test prior to execution of the loop statements, and the latter has its 
test at the end of the loop. Nesting of the DO groups is indicated by the 
indentation of lines. 



1 

2 

3 

4 

5 

6 

7 
8 
9 
10 
11 
12 
13 
11 
15 
16 
17 
18 



KEYBOARD. INTERPRETER: 
PROCEDURE; 
OLDKEY - NULL. 
GO - FALSE; 

DO UNTIL GO = TRUE: I' LOOP UNTIL DONE WITH INPUTS ' 
DO WHILE NOTREADY(KEYBOARD) ' TRUE; 



CALL CURBLINK; 

OLDKEY ■ NULL, 

TIMEOUT LONGWAIT; 
END; 

KEY = INPUT(KEYBOARD); 
CALL DECODE; 

CALL REPEATWAITITIMEOUTI; 
IF KEY - OLDKEY THEN 

TIMEOUT SHORTIMEWAIT; 
OLDKEY = KEY; 
END; 
CLOSE KEYBOARD INTERPRETER; 



/• THIS LITTLE LOOP WAITS '/ 

/• FOR A KEYSTROKE AND BLINKS ■ 

/■ THE CURSOR ALL THE WHILE '/ 

/• WHEN READY, READ KEYBOARD 

/■ EXECUTE COMMAND V 

/■ DON'T LOOK TOO SOON '/ 

/• SHORT DELAY AFTER FIRST V 

/' TWO OPERATIONS DONE •/ 



Subroutines Referenced by KEYBOARD INTERPRETER: 

NOTREADY = a function subroutine (also referenced by INPUT) 
which is used to control an idle loop. It returns FALSE as its value if 
the selected device (in this ease, KEYBOARD) is ready for input, and it 
returns TRUE as its value otherwise. 

CURBLINK = a subroutine which "blinks" the cursor on for a fixed 
period of time, followed by a fixed period of "off" time. Since it must 
be called each time a single blink is required, this implements the 
"active control" feature mentioned in LIFE Line 1. 

INPUT = a function subroutine which returns the current input data 
value for the selected device (in this case, KEYBOARD). INPUT has its 
own wait loop referencing NOTREADY - which for KEYBOARD_ 
INTERPRETER is redundant, but is not redundant in general. 

DECODE = the major subroutine of KEYBOARD INTERPRETER. 
This routine analyzes KEY based upon tables and the previous inputs to 
the program from the operator. Using this analysis it will select the 
appropriate subroutine to execute. These "command subroutines" will 
in turn affect LIFE program data and the course of the LIFE program's 
execution. 

REPEATWAIT = a subroutine designed to call CURBLINK a number of 
times specified by TIMEOUT. This implements a delay between 
multiple responses to the same key held down continuously. 

Data (8-bit bytes) used locally by KEYBOARD, INTER- 
PRETER: 

OLDKEY = 8-bit value of the last previous keystroke. 

NULL = 8-bit value of a null key pattern as read from the keyboard. 

TIMEOUT = 8-bit value of the current repeat key time delay. 

SHORTIMEWAIT = the timeout parameter used after the first delay in 
a multiple input of the same key. This specifies the rate of rapid motion 
of the cursor under manual control. 

LONGTIME WAIT = the value of the timeout parameter used for the 
first delay following a key entry. A longer wait is required at first to 
avoid false duplication of keystrokes for heavy-handed players of the 
game. 

Data (8-bit bytes) used by KEYBOARD _INTERPRETER and 
shared with the whole program. See Table II for explanations. 

GO, DONE, TRUE, FALSE, KEYBOARD, COMMAND, KEY 



50 



extent of the next run. Since 
this application uses 8-bit 
data, the limit is 255 
generations of LIFE at 
present. 

Figuring Out What the User 
Said 

The K E YBOARD_ 
INTERPRETER routine 
serves the function of 
controlling the input of 
information to these software 
register and to the 
LIFEBITS grid. The routine 
itself is a loop which executes 
over and over until the user is 
ready to run the 
GENERATION algorithm for 
one or more generations. The 
KEYBOARD. 
INTERPRETER terminates 
for one cycle of LIFE when 
the user inputs a "G" control 



command which is 
interpreted semantically as 
"GO generate N generations". 
The flow chart of the 
KE YBOARD_l NTER- 
PRETER logic is illustrated in 
Fig. 2, with the equivalent 
procedure-oriented language 
version shown in Fig. 3 as a 
detailed reference. In Fig. 2, 
line numbers are provided for 
comparison to Fig. 3. 

Execution of the 
KEYBOARD_INTER- 
PRETER begins with some 
initialization statements. The 
values of GO and OLDKEY 
are set at the start of 
execution (lines 3 and 4). 
These values will be changed 
during execution of the 
KE YBOA RD_INTER- 
PRETER based upon input 
data. OLDKEY is used to 



detect duplications of 
keyboard input which occur 
when a key is held down for 
continuous operations. After 
a given KEY is held down 
continuously for two 
operations, the repetition 
goes into a high speed mode 
with SHORTIMEWAIT 
controlling the delay between 
operations. GO is the control 
variable which is used to 
govern whether or not the 
loop is to continue — it is 
initialized to FALSE and will 
be changed to TRUE when 
the "G" user command is 
decoded. 

Programs Are the Willing 
Servants of the Noble User? 

Interaction of 
programmed computers with 
human beings is often a 



waiting game. This waiting 
game is aptly illustrated in 
the loop which checks for 
user input keystrokes at lines 
6 to 10 of the KEYBOARD 
.INTERPRETER routine. 
The function NOTREADY 
(KEYBOARD) is a notational 
convention used to indicate a 
test for the keyboard ready 
condition. Like a ready and 
willing servant, the computer 
program keeps marking time 
in this loop until the user — 
you or I - has given it a 
character to digest. Two 
statements are included in 
this loop for the purpose of 
coordinating multiple 
keystroke conditions: Setting 
OLDKEY = NULL is used to 
re-establish a null history if 
the program ever has to wait 
(it never waits when keys are 



Table I. ASCII Command encoding for the LIFE application. This is an initial specification of the command codes used to control the 
KEYBOARDINTERPRETER routine's effect. The command table locations go up by three as in Fig. 4. No addresses for the command 
subroutines are given yet — these will be filled in when the program is compiled for your computer. Command table locations and command 
characters are given as hexadecimal numbers. 



Command Table Command 
Location Character 

00 xx 



03 



47 



ASCII Command 

Key Subroutine 

??? DEFAULT 

G RUN 



Meaning of the Command (its 'semantics") 

The first table position is the "default" routine position, which is called 
when no other matching key is found in the table search. 

The "run" command which sets a flag called GO in order to end the 

KEYBOARD_ll\ITERPRETER and have LIFE call the GENERATION 
routine. 



06 



09 



0C 



OF 



12 



15 



18 



IB 



49 

53 
52 
58 
59 
4E 
43 

45 



I INITIALIZE 



SAVELIFE 



RESTORELIFE 



SETXLOC 



SETYLOC 



N SETNGEN 



CLEARS 



LIFEDONE 



The "initialize" command to set up the screen with predetermined 
patterns selected by additional keystrokes. 

The "save" command to dump the current screen content onto a 
waiting audio cassette or other mass storage device. 

The "restore" command to recover a screen pattern previously saved 
by "S". 

The "set X" command to explicitly set the horizontal cursor location, 
XCOL. 

The "set Y" command to explicitly set the vertical cursor location, 
YROW. 

The "set N" command to explicitly set the generation count for 
subsequent execution with the "G" command. 

The "clear screen" command to wipe out all data and place the cursor 
at the center. CLEARS requires confirmation with a second S key 
stroke to avoid accidental clears. 

The "done" command is an E followed by an L (for End Life.) The 
second character confirmation is checked by LIFEDONE. 



Note that the ASCII characters to 9 are used to define the "current input" maintained by software in ENTRY. ENTRY may then be 
transferred to N, XCOL, or YROW by the N, X and Y commands respectively. 



51 



held down continuously). 
TIMEOUT = LONGTIME- 
WAIT re-establishes a longish 
debounce period between key 
interpretations following a 
series of continuous inputs. 
The program of course thinks 
that if a key is not ready 
upon restarting the main loop 
at line 6 it could not possibly 
be a repeat. While idling and 
waiting for your interactive 
whims, the computer 
program is not completely 
devoid of useful work. It calls 
CURBLINK once each time 
around the wait loop in order 
to flash the cursor actively on 
the screen. 

Finally, after some time of 
unspecified duration, you 
make up your mind to input 
a key. This has one major 
effect upon the program: The 
next time around the loop at 
the test of the WHILE 
condition, a result of FALSE 
ends the loop. Execution 
then flows from the DO 
WHILE (line 6) to line 11 
where the KEY is read from 
the waiting keyboard device 
by a subroutine called 
INPUT. 

With KEY defined, 
DECODE is the next item on 
the agenda. DECODE is one 
of the major subroutines of 
KE YBOARD_INTE.R- 
PRETER, a routine which 
takes KEY and compares it to 
a COMMAND table. The 
result of the COMMAND 
table search is execution of a 
"command subroutine" if a 
match is made, or execution 
of a DEFAULT routine if no 
match to KEY is found. 
Upon return to 
KEYBOARD_INTER- 
PRETER (all subroutines by 
nature return to the caller 
except in very rare cases), the 
flow of control reaches the 
REPEATWAIT call using the 
current value of TIMEOUT. 

During normal execution 
of single isolated commands, 



the TIMEOUT value is 
LONGTIMEWAIT - which 
might be chosen to be from 
0.1 to 0.5 seconds. This 
TIMEOUT sets the minimum 
time between the first 3 
keystrokes of a repeated 
sequence. But, after two long 
delays have been executed, 
the match of OLDKEY = 
KEY is detected at line 14 
and TIMEOUT is changed to 
SHORTIMEWAIT allowing a 
speedy repeated motion case. 
SHORTIMEWAIT might be 
chosen in the 0.05 to 0.1 
second range for rapid 
motion. The values of these 
two motion control constants 
are left unchosen for now, 
and can be figured out as 
binary integers to be used in 
REPEATWAIT when details 
of the CPU and 
REPEATWAIT routine are 
filled in. Note that if fast 
operation is desired 
immediately after the second 
operation of a repeated 
sequence, then line 1 3 of Fig. 
3 should be moved to a 
location between lines 1 5 and 
16. 

In order to control the 
repeat logic, the statement 
OLDKEY=KEY is executed 
at line 16 so that the last 
input will be retained for 
comparison purposes the next 
time around. 

The KEYBOARD. 
INTERPRETER routine 
finishes up with the CLOSE 
statement of LIFE line 18, 
which stands for the end of 
the routine and return to its 
caller. There is one and only 
one caller of this routine, the 
LIFE program itself, 
illustrated in Fig. 3 of LIFE 
Line #2. 

It's All in DECODE of the 
LIFE Program 

When giving the details of 
the KEYBOARD_INTER- 
PRETER logic, the principle 



While idling and waiting 
for your interactive whims, 
the computer is not com- 
pletely devoid of useful 
work. It calls CURBLINK 
once each time around the 
wait loop in order to 
seductively flash its cursor 
on the screen. 



Fig. 4. Decoding by multiple conditional tests. This method of 
decoding keystrokes and activating routines in software is most 
efficient when a small number of possible commands is involved. 




52 



Fig. 5. Typical code for a single conditional test in the scheme of Fig. 4. 
The example here is using Motorola 6800 system mnemonics. This 
example assumes accumulator A is set up with the character being 
decoded. 



of keeping the program 
design locally simple results 
in a CALL DECODE at line 
12. Whenever some 
subroutine is left unspecified 
except for its inputs (KEY 
for DECODE) and its outputs 
(a command subroutine's 
execution), sooner or later 
the details must be filled in. 
In designing a DECODE 
algorithm to fill in this set of 
details, there are numerous 
alternatives. For high order 
language aficionados, 
something called a 
"computed GO TO" 
(FORTRAN) or "DO CASE" 
(PL/1 family languages such 
as XPL or PL/M) would 
suffice following a table 
search. However, for this 
particular application, a 
slightly lower level approach 
is justified to conserve 
memory. 

Two major alternatives 
come to mind as possible 
ways to map an input KEY 
value into the execution of a 
selected subroutine. The 
simplest (least elaborate) 
"straightforward" approach is 
the method of multiple 
conditional tests. This is 
illustrated schematically in 
Fig. 4's flow chart, and in a 
concrete form in Fig. 5's 
example of a segment of the 
typical conditional test. In 
this approach, each possible 
command code is tested in 
turn by the routine. 
Eventually, all the explicit 
possibilities will have been 
exhausted if no match is 
found. Then, if "none of the 
above" match the KEY input, 
a DEFAULT routine is called. 
The main advantage of this 
approach is also its 
disadvantage: It is a plodding 
and straightforward approach 
which squanders memory. 
While the code's intent is 



obvious, it requires — in the 
example of Fig. 5 — a total of 
8 bytes per test. 

There should be a better 
way — comparisons and 
branches are repeated in this 
method. The segment of 
generated code and its 
corresponding procedure- 
oriented language version in 
Fig. 5 shows four instructions 
which are repeated over and 
over but with varying data 
(the character being 
compared and the address of 
the subroutine). Why not put 
the instructions in only once 
and tabulate the variable 
data? There might be a saving 
of memory if this table driven 
approach is used instead. 

Fig. 6 illustrates the 
concept of an alternative 
structure, the "command 
table," which will result in a 
lower memory requirement 
once the number of 
commands to be tested 
exceeds some break even 
point. In this concept, the 
changing data for each test is 
stored in the table, and the 
program to go along with it 
uses a looping technique to 
scan that table. The changing 
data for tests comprises: 

— The command character. 
This is the keyboard code 
which is matched against 
the actual KEY input. 

— The command 
subroutine. This is the 
address of the subroutine 
which will be called if KEY 
matches the corresponding 
command character. 

The table is organized in 
3-byte groups consisting of a 
command character followed 
by its subroutine address. 
Note that on first inspection, 
this form of DECODE 
requires only 3 bytes of 
storage per test versus the 8 
bytes in the example of Fig. 



Byl 


es Mnemonic 


Comment 


2 


CMPA # 'G 


Compare A to literal 


2 


BNE *+4 


Branch around JSR and RTS 


3 


JSR GROUTINE 


Call the G subroutine 


1 


RTS 


Return from decoder rather than 
continue the testing 


8 


= Total number of bytes per test. 


This is the "generated code" 
procedure-oriented language 


of the following statements in the 
used for LIFE Line examples: 


IF 


KEY = 'G' THEN 

DO; /* HAVE MADE A MATCH */ 

CALL GROUTINE; 

RETURN; /* FROM DECODE COMPLETELY */ 
END; 



Relative 
Address 



3(n+1l 



Default Address 



Address of "G" 
Command Subroutine 



Address of "H" 
Command Subroutine 



Fig. 6. The Command Table 
Concept. By storing the character 
(keystroke) being decoded, 
followed by the address of its 
routine, only three bytes need be 
used for each routine which could 
be decoded. Allowing for the 
overhead of a longer decode 
algorithm (specified once), the 
command table method will prove 
more compact when the number 
of commands get larger than four 
or five. 



53 



Fig. 7. The Command Table DECODE routine specified in a procedure 
oriented language. 



1 DECODE: 

2 PROCEDURE; /• TO FIGURE OUTWHAT USER SAID »/ 

3 /• COME HERE WITH THE KEY TO THE COMMAND '/ 

4 DO FOR I = 3 TO LENGTH(COMMAND) BY 3; /* SCAN TABLE '/ 

5 IF KEY = COMMAND(I) THEN 

6 DO. /' WOW!! I GOT A MATCH I GOT A MATCH! V 

7 I = 1 + 1;/* POINT TO ADDRESS ENTRY */ 

8 CALL CALLXICOMMAND(II); 

9 /- NOTATION FOR CALL OF SUBROUTINE. INDEXED •/ 

10 RETURN; 

11 /* THIS FORCES EXIT FROM DECODE '/ 

12 END; 

13 /' ONLY GET HERE IF NO MATCH IN TABLE »/ 

14 CALLCALLX(COMMANDd));/ - CALL DEFAULT FROM TABLE »/ 

15 END; 

16 CLOSE DECODE; 

Data (8-bit bytes) used locally by DECODE: 

I = temporary used for loop control and indexing. 

Data (8-bit bytes) used by DECODE but shared with the 
whole program. For details see Table II . 

COMMAND, KEY 

Subroutines referenced by DECODE: 

DECODE does not use any "real" subroutines, but does use the 
following two notational conventions which look like subroutines. 

LENGTH(COMMAND) stands for the length (in bytes) of the 
COMMAND table. When you know what it is, you put in the value. 

CALLX(X) is used to denote using the two bytes starting at the 
address X as the address of a subroutine to be called. This is an 
indexed subroutine call effectively. For a Motorola 6800 CPU, this 
would be performed by an LDX instruction indexed off the 
COMMAND table position, followed by a JSR instruction with the 
indexed addressing mode. 



5. For a 10 command table, 
this would be a 50 byte 
saving at first inspection. 
However, the 50-byte figure 
does not take into account 
the longer looping routine 
required to scan the table and 
indirectly jump when a match 
is found. But for 10 
commands (the number 
found in Table I) this 50 byte 
saving potential goes a long 
way. I expect the actual 
DECODE routine of the table 
driven variety to be 



considerably less than 50 
bytes in length when it is 
generated for the 6800 
system instruction set used as 
the straw-man in Fig, 5. I'll 
leave the final conclusion on 
that to a later LIFE Line. 

There is an additional 
advantage to be obtained 
from the table driven 
method. This is an advantage 
which concerns some of the 
finer points of programming: 
The table driven method 
results in "pure code" in 



which potentially variable 
data is completely segregated 
off in the table. This achieves 
an often desirable end of 
separating data from 
instructions. In the multiple 
conditional test version, the 
data of the DECODE is 
embedded right in the 
instruction stream, both as 
the literal value of the 
character being tested and as 
the address of the routine 
being selected. If I want to 
modify the multiple 
conditional test version, I 
must certainly recompile or 



reassemble the whole routine 
(a pain in small systems 
work). In contrast, to modify 
the table driven version, I 
only have to alter the table 
itself, and the variable which 
specifies the table's length. 
But this is a minor point in 
addition to the major 
memory conservation 
argument for the table driven 
approach. 

The actual algorithm for 
DECODE is shown in a 
procedure-oriented language 
in Fig. 7. The scan of the 
table is a DO FOR loop with 



Notes on Notation: 

Concerning Indentation: The listings of procedures for 
the LIFE program make use of an indentation 
convention to help show the structure of the routines. 
The significance of the indentation is that it shows the 
opening and closing of various local software 
constructions and in so doing helps convey the meaning 
of the program to human readers. Note how the 
statements from line 7 to line 11 of DECODE in Fig. 7 
are indented one level compared to the DO (line 6) and 
END (line 12) statements. This indentation shows that 
lines 7 to 11 are part of the DO . . . END construction 
which is executed if the test on line 5 gives a true result. 

The notation "/*" followed by arbitary remarks and 
then a "*/" is the "comments" convention used in these 
examples. This convention is stolen from the PL/1 
family of languages. 

Concerning names of variables: With each procedure 
specified in LIFE Line, data is separated into two 
categories: Local data is used only within the procedure 
question. Local data may have a name which duplicates 
names used in other procedures, but is always qualified 
by its local nature. Thus "I" in GENERATION (Fig. 6, 
LIFE Line 2) is a different data location in memory than 
the -I" in DECODE (Fig. 7, LIFE Line 3). Data 
shared with the rest of the program, which is often 
called global data in programming terminology, is in 
contrast defined universally for LIFE. Global data is 
summarized for LIFE in Table II. Thus whenever KEY is 
referenced (as in KEYBOARD_INTERPRETER or in 
MOVECURS) the same data is intended, since these have 
been classified as shared or global in the notes 
accompanying the program listings. 



54 



the index, I, running from 3 
(the first entry is reserved for 
the default) to the length of 
the table by 3. When a match 
is found, the 1 6-bit address in 
the table is used for an 
indirect subroutine call (lines 
7 and 8). For a Motorola 
6800 system, this would be 
accomplished by an indexed 
JSR instruction after loading 
the index register from the 
table. When the selected 
command subroutine returns 
to DECODE (as would any 
well structured subroutine in 
the same circumstance), the 
RETURN statement is 
executed causing an exit from 
DECODE and resumption of 
the KEYBOARD^ 
INTERPRETER at the calling 
point. If no match is found, 
the loop eventually runs out 
and line 14 of Fig. 7 is 
reached, where the 
DEFAULT routine is called. 



This is shown notationally in 
a general purpose form with 
reference to the command 
table, but in generating the 
code for the statement of line 
1 4, a simple call to 
DEFAULT might be 
substituted. (If the generality 
of the DECODE routine is to 
be preserved for possible use 
with other command tables, 
this optimization would not 
be possible.) 

What about data for the 
COMMAND table? Table I 
provides a preliminary answer 
to this question by giving a 
list of command table entries 
including relative location, 
the corresponding character 
code, the ASCII key which 
invokes the command, the 
name of the subroutine and a 
verbal description of the 
subroutine. This table will be 
used as the basis for creating 
a detailed data table when the 



actual programs of LIFE are 
generated for a particular 
computer in a future LIFE 
Line. For now, Table I serves 
to list the areas which remain 
to be covered in the 
discussion of the 

KEYBOARD_INTER- 
PRETER and all its 
subroutines. 

LIFE Line 4 will continue 
the presentation of the 
KEYBOARD^INTER- 
PRETER portion of the LIFE 
program. To fill out the 
remaining portion of the Tree 
of LIFE, the next installment 
includes the integration of 
graphics control commands 
into the KEYBOARD. 
INTERPRETER and the first 
hardware details of LIFE — a 
simple circuit which 
combines an ASCII keyboard 
input with the special 
purpose controls for an 
interactive cursor. ■ 



Does Anyone Know What 
Happened to Robert T. 
Wainwright? 

This series of articles 
inadvertantly duplicated 
the name of Robert T. 
Wainwright's LIFELINE 
newsletter, published 
through 1973. Thanks to 
Bob Albrecht of People's 
Computer Co. for sending 
us his copy of LIFELINE'S 
last issue. Does anyone 
know where Mr. 
Wainwright is now (he's no 
longer at the address given 
by Charles A. Dunning Jr. 
in the Letters column), 
and is LIFELINE still 
being published? 



Table II. Global Data. Data which is shared by an entire program or application is often called "global". The word global is used to indicate the 
widespread effects of such data in the program's execution. Many procedures will alter and change such data. This table summarizes the global data 
variables of the LIFE application as used in procedures given in LIFE Lines #2 and Jf3. 



COMMAND = the table of commands interpreted by DECODE, 
containing the ASCII codes of command keys and the addresses of the 
appropriate command subroutine. The format of this table is illustrated 
in Fig. 6. The information content, in preliminary form, is found in 
Table I. 

DONE = the variable used to control continued execution of the main 
LIFE routine (see LIFE Line #2, Fig. 3). 

ENTRY = the entry register used to receive numeric ASCII digits, after 
weighting the previous value in a BCD fashion. While the entry to 
ENTRY of new digits is done in a BCD manner (multiplying by 1 then 
adding the digit's value) the content of ENTRY is a binary number of 
8-bit precision with values to 255 and is thus not itself BCD. (BCD = 
"binary coded decimal.") 

FALSE = the value "0" (00 hex, 000 octal, 00000000 binary). This 
name is used to indicate the software equivalent of a hardware gate 
input wired to logical zero. 

GO = the Hag (value is TRUE or FALSE) which controls continued 
execution of KEYBOARD_INTERPRETER. 

KEY = the 8-bit data area which receives keyboard inputs. 

KEYBOARD = the logical unit number of the keyboard I/O device. 
This is a bit pattern which specifies the device one is talking to. 

LIFEBITS = the object of the whole exercise - an array of 64 by 64 
bits stored as 64 by 8 bytes. 

N = the variable used to control the number of generations to be 
evolved by LIFE before returning to KEYBOARDINTERPRETER 
graphics control. 



NCMIN = current minimum column index of live cells. 

NCOLMAX = maximum column index of live cells for active area 
optimization. 

NCOLMIN = minimum column index of live cells for active area 
optimization. 

NROWMAX = maximum row index of live cells for active area 
optimization. 

NROWMIN = minimum row index of live cells for active area 
optimization. 

NRMAX = current maximum row index of live cells. 

NRMIN = current minimum row index of live cells. 

TEMP = 2 by 8 array of bytes containing two 64-bit rows of cells. 

THAT = previous line copy index to TEMP used in GENERATION (see 
LIFE Line #2, Fig. 6). THAT should always have a value of 1 or 0, 
opposite of TFI1S. 

THIS = current line copy index to TEMP used in GENERATION (see 
LIFE Line -#2, Fig. 6). THIS should always have a value of or 1. 

TRUE = the value "255" (FF hex, 377 octal, 11111111 binary). This 
name is used to indicate the software equivalent of a hardware gate 
input wired to logical one. 

XCOL = the current cursor position in the horizontal (column) 
direction. 



NCMAX = current maximum column index of live cells. 



YROW = the current cursor position in the vertical (row) direction. 



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ADDRESS . 



ORGANIZATION . 



CITY/STATE/ZIP- 



Flip Flops 



Exposed 



by 

William E. Browning 
5J6 N. 95th E. Ave. 
Tulsa OK 74155 



One of the important 
building blocks in working 
with transistor-transistor logic 
is the flip flop. It is important 
to understand this building 
block if you desire to use it in 
projects of your own. 

The two most common 
types of flip flops are known 
as the JK flip flop and the D 
flip flop. 

JK Flip Flop 

The JK flip flop has four 
or five inputs and one or two 
outputs. The input pins are 
labeled J, K, CLOCK, 
CLEAR and PRESET, and 
the output pins are labeled Q 
and Q which is often 
pronounced as "Q bar" or 
"not Q". A typical block 
diagram of a JK flip flop is 
shown in Fig. 1 . 

The outputs (Q and Q) can 
be in one of two states: High 
(logic 1) or low (logic 0). In 
general, if the Q output is 
high then the Q output is 
low, and vice-versa, if the Q 
output is low then the Q 
output is high. We will often 
refer to the Q output only 
since we know that Q will be 
the opposite. So if we say 



that the output is high it 
means that Q is high and Q is 
low. However, this is not 
always so; on some flip flops 
you may find a Q output 
only, and, as you will see 
further below, both outputs 
may be high or low under 
specific conditions. 

Asynchronous Inputs 

Now that we know about 
the output states, let's discuss 
the inputs to give us the 
desired outputs. The PRESET 
and CLEAR pins are known 
as asynchronous inputs. 
Asynchronous means that 
these inputs do not depend 



upon the timing derived from 
the clock pulses. 

With almost all flip flops a 
low PRESET will take Q to 
high, and a low CLEAR will 
take the Q to high. With both 
PRESET and_ CLEAR low 
both Q and Q will be high. 
This is the only time when Q 
and Q are not opposite from 
each other. If both PRESET 
and CLEAR are high, then 
the control of the output is 
given to the J, K and CLOCK 
inputs. The relationship 
between the asynchronous 
inputs and the output is 
shown in the truth table of 
Fig. 2. 



(INPUTS) 





6 






CLEAR 
J Q 












(OUTPUTS) 




CLOCK 

K Q 

PRESET 














f 





Fig. 1. The JK flip flop block diagram. 



58 



PRESET 


CLEAR 




Q 


Q 


L 


L 




H 


H 


L 


H 




H 


L 


H 


L 




L 


H 


H 


H 




NO CHANGE 



Fig. 2. Truth table of a JK flip 
flop responding to preset and 
clear. 




Synchronous Inputs 

The J and K inputs are 
synchronous inputs. 
Synchronous means that they 
depend on the CLOCK for 
operation. 

For most JK flip flops a 
simple set of rules apply to 
the synchronous inputs, but 
not all flip flops are standard. 
There are several variations 
on the timing when the chip 
accepts inputs and when the 
output changes. 

The most c ommon 
input-output relation is 
known as the rising-edge 
triggered flip flop. The 
rising-edge triggered flip flop 
derives its name from the fact 
that it changes its output 
states only when the CLOCK 
level rises from low to high. 
Of course, the output states 
depend on the configuration 
of the J and K inputs. Fig. 3 
illustrates the changes of the 
Q pin depending on the levels 
on the J and K pins: When 
both J and K are low, Q does 
not change; when both are 
high, Q changes into its 
opposite state; with J being 



low, and K being high, Q 
assumes a low level, and when 
J is high, but K is low, Q will 
take on a high level. 
Remember, though, that this 
change can happen only if the 
CLOCK input rises from low 
to high, and, as was shown in 
conjunction with Fig. 2, 
when both PRESET and 
CLEAR are high. 

The less frequent type of 
input-output relation is 
known as the falling-edge 
triggered flip flop. This flip 
flop resembles the first, 
except that the output 
changes to the condition 
selected by the J and K 
inputs when the CLOCK level 
falls from high to low. 
Everything else remains the 
same. 

It is easy to change the 
operation of a falling-edge 
triggered flip flop to that of a 
rising-edge triggered flip flop. 
All that needs to be done is 
to invert the input to the 
CLOCK. The inverter shown 
in Fig. 4 changes a high level 
to a low level, and vice versa; 
a rising-edge triggered flip 
flop can be changed to a 



Fig. 4. Inverting the clock input 
converts rising edge-triggered 
operation into negative edge- 
triggered operation and vice versa. 



I 



OUTPUT rOUTPUT ["OUTPUT 
CHANGES CHANGES CHANGES 






CLOCK 
PULSE 



^J 














V 


\ 


\ 


INPUT 


NEW INPUT 


NEW INPUT 


ACCEPTED 


ACCEPTED 


ACCEPTED 



Fig. 5. Timing of a negative clock 
pulse master/slave flip flop. 



INPUT NEW INPUT 
ACCEPTED ACCEPTED 



V 



^ 



NEW INPUT 
ACCEPTED 



CLOCK 
PULSE 



J~L 



J~L 



OUTPUT 
CHANGES 



Fig. 6. Timing of a positive clock 
pulse master/slave flip flop. 



Loiitpiit V. 



-OUTPUT 
CHANGES 



OUTPUT 
CHANGES 



»n 




t„ + 1 


J 


K 




Q 


L 


L 







L 


H 




L 


H 


L 




H 


H 


H 








Fig. 3. Truth table of a JK flip 
flop for synchronous (clocked) 
operation. 



falling-edge triggered flip 
flop, and vice versa, by means 
of the inverter. 

A third type of input is 
known as the negative clock 
pulse master/slave flip flop. 
With this flip flop the inputs 
are applied to the J and K 
pins when CLOCK goes low 
and change their outputs 
after the rising edge of the 
clock pulse (see Fig. 5). 

The clock pulses should be 
made as short as possible and 
the time between clock pulses 



as long as possible. This will 
i n c re ase immunity to 
alternating current noise and 
accommodate all ripple delay 
between clock pulses. 

A fourth type of input is 
the positive clock pulse 
master/slave flip flop. This 
flip flop accepts inputs when 
CLOCK goes high and 
changes output when CLOCK 
goes low (see Fig. 6). The 
pulses should be made as 
short as possible for the 
above mentioned reasons. 



59 



+ 5 



PRESET CLOCK 



Ik 


13 


12 








ill 




10 




9 


8 












































rt 






> 


P 
K Q 

CLOCK 

J Q 
C 


















L, 


> 














V 




























T 


2 


3 








4 




5 




6 


7 



GND 



Fig. 7. Pinout of the 7472 IC, a positive clock pulse master/slave flip 
flop. (Top view ) 



+ 5 V 



PRESET CLOCK K2 



Kl 



K# 



1,4 


13 


12 




II 




10 




9 


8 












































t 1 


) 




oN 




) 


P 
K Q 
CLOCK 
J Q 

c 




j\ v 










N 


/ 




V 




J 














\ 


> 


























T 


2 


3 




4 




5 




6 


7 



N.C. CLEAR J I 



J2 



J* 



GND 



Fig. 8. Pinout of the 7470 IC, a positive edge triggered flip flop. (Top 
view) 



l 


A 
14 




Q 


A 
13 


C 


A 
12 


GND 

In 




K 


B 
10 


2 B 

9 




C 


B 
8 








































r 












-o 


O K3 

3 

"3 O i£ 




o lo 
o 

3 

* O -3 


<-> 


> 








1 


1 






^ 


T 






















































1 






2 




3 


|4 






5 


6 






7 



CL0CK A CLEAR A K A V cc CLOCKg CLEARg J B 

+ 5V 



Fig. 9. Pinout of the 7473 IC, a dual positive clock pulse master/slave 
flip flop. (Top view ) 



Variations on the Four Flip 
Flops 

One of the confusing 
aspects with flip flops is that 
they differ in the logic 
controlling the J and l< 
inputs. Some have AND/OR 
logic circuits accepting several 
distinct inputs, and others 
have an inverter before the J 
or K inputs. 

If wc look at some 
diagrams of flip flop ICs, 
their operation will be easier 
to understand. 

The 7472 in Fig. 7 is a 
single JK flip flop of the 
positive pulse master/slave 
type. 

The 7472 uses gates on the 
J and K inputs. In order to 
get a high level on the J input 
of the flip flop a high on all 
three J inputs of the IC (pins 
3, 4 and 5) and the clock (pin 
12) is required. In a similar 
manner, a high on the K 
input of the flip flop is 
obtained with a high on all 
three K pins (pins 9, 10 and 
11) and the clock of the IC. 

If you have only one J 
input, connect all three J pins 
together, or connect two of 
the J inputs to high, and use 
the remaining input for the 
data input. The same holds 
true for the K inputs. 

The 7470, shown in Fig. 8, 
is a single JK flip flop of the 
positive-edge triggered type. 

The 7470 has identical 
gates and inverters on the J 
and K inputs. For example, 
to get a high level on the J 
input of the flip flop a high 
on J1 and J2 (pins 3 and 4) 
and a low on J* (pin 5) must 
be received. A low level on 
pin 5 is inverted to a high on 
the input to the gate. 

If you do not need J* or 
K*, connect them to ground. 
If you do not need J1, J 2, K1 
or K2 connect them to high. 

The 7473 IC is a dual JK 
flip flop of the positive pulse 
master/slave type. Fig. 9 
shows that this IC does not 
use gating on the J and K 
inputs. 

The two flip flops operate 



separately from each other 
having only the +5 volt Vcc 
and ground in common with 
each other. You may also 
have noticed that Vcc is on 
pin 4 and ground on pin 11. 
This is not the same as on 
most 7400 ICs which have 
Vcc on pin 14 and ground on 
pin 7. So check your 
connections before you apply 
power. 

There are no PRESET 
inputs to the chip, in order to 
allow a 14 pin package. 

If you do need the 
PRESET on a dual JK flip 
flop, use the 7476 available in 
a 16 pin package. It is shown 
in Fig. 10. It has independent 
CLEAR and PRESET pins, 
whereas in the 74H78 of Fig. 
11 the CLOCK and PRESET 
pins, respectively, are 
connected. The 74H78 comes 
in a 14 pin package. 

In many circuits the same 
clock operates many flip 
flops and several flip flops are 
cleared at the same time. The 
74H78 is well suited for these 
needs because it saves on the 
number of external 
connections, saves on the size 
of the IC package, and the 
number of pins. 

D Flip Flop 

Let's make one small 
modification to the JK flip 
flop: An inverter connects 
the K input to the J input as 
shown in Fig. 12. 

If J is high then K will be 
low, and if J is low, K will be 
high. Since there is only one 
synchronous input instead of 
the two, let's call it the data 
input or D input. 

Some flip flops have this 
modification built into an IC 
and are referred to as D flip 
flops. A typical block 
diagram of a D flip flop is 
shown in Fig. 1 3. 

The truth table of the D 
flip flop is shown in Fig. 14. 
Remember that the PRESET 
and CLEAR must be high, as 
discussed in connection with 
Fig. 2. The truth table for 
asynchronous inputs applies 
also to the D flip flop. 



60 




CLOCK A PRESET A CLEAR ft J A 



V CC 
+ 5 



Several ICs employ the D 
flip flop. One of these is the 
7474 dual D flip flop. Since 
only one pin is needed for 
data entry to each flip flop 
both preset and clear 
capability can be provided in 
a 1 4 pin package. The 
diagram of the 7474 is shown 
in Fig. 15. 

The 7475 IC uses a D flip 
flop which is called a latch 
because the CLEAR and 
PRESET pins are absent. The 



clock b preset b clear b reduction in pins has been 



carried one step further by 
combining two CLOCK pins 
each. Therefore it is possible 
to put four latches on one 16 
pin IC; the 7475 quad latch is 
shown in Fig. 1 6. 

This short introduction to 
flip flops, latches and 
integrated circuits should 
help your understanding of 
this building block. With a 
thorough understanding of 
these circuits, you will be 
well on your way to designing 
your own equipment. ■ 



Fig. 10. Pinout of the 7476 IC, a dual flip flop similar to the 7473 but 
having both PRESET and CLEAR. (Top view ) 



+ 5 

V„„ PRESET CLEAR 

A ABB 



CLOCK K 

A8B B 





CLEAR 



Fig. Ji. And still another combination - the pinout of the 74H78 has 
14 pins with common CLEAR and CLOCK, and separate PRESET pins. 



Fig. 15. The pinout of the 7474 dual D flip flop. (Top view ) 




CLEAR 
D Q 



CLOCK Q 
PRESET 



Fig. 12. Making a "D" flip flop Fig. 13. The block diagram of a D 
out of a "JK" with an inverter. flip flop. 
(Top view ) 



»n 


»n+l 


D 


Q Q 


L 


L H 


H 


H L 



— CLOCK 





Q 


A 
16 


Q 


B 

15 




C 


B 
14 




A8B GND 
13 ||2 


Q 


c 

1 




C 


»C 

10 




o 


D 

3 
























































- 


~l 
























Q Q 
9 D 




CLOCK Ol 






CLOCK Ol 
o o 




Q Q 

d ; 
















1 






































- 


















1 




2 






3 




4 


| 


5 




6 






7 






3 



D D CLOCK V r , 



+ 5V 



Fig. 14. Truth table of a D flip 
flop. 



Fig. 16. Pinout of the 7475 latch (or register) circuits. (Top view ) 



61 



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63 



Read Only 
Memory Technology 



Kead Only Memories are a useful element of the hardware 
of microcomputer systems. This month, Don Lancaster pro- 
vides information on Read Only Memories - a tutorial article 
taken from Chapter 3 of his forthcoming book, TV Typewriter 
Cookbook, to be published by Howard W. Sams, Indianapolis, 
Indiana. 



by 

Don Lancaster 

Synergetics 



Low cost and compact 
memory components are the 
key to simple and reasonable 
TV typewriter and 
rriicrocomputer systems. 
Today there are many ICs 
available that will cram 
thousands or more bits of 
storage in a single package at 
costs of a fraction of a cent 
per bit. The problem is to 
pick the memory components 
that are the cheapest, the 
easiest to use, and the ones 
with the fewest unpleasant 
surprises. 

What does memory do for 
us? Well, it remembers. If it 
remembers extremely well it 
can be used as a fixed logic 



element or to store an 
often-used software routine. 

An important example of 
this is the character generator 
memory that converts our 
ASCII code into a group of 
dot patterns suitable for 
video use. The same type of 
memory might be used to 
change the keyboard switch 
closures and shift 
combinations into selected 
ASCII codes. We also use 
permanent memory for code 
conversions such as going 
from ASCII to SELECTRIC, 
and permanent memory is 
usually used to store the 
program and control 
commands for an external 



microprocessor or 
minicomputer system. 

This particular type of 
memory is called a read only 
memory, or ROM. Once 
taught, it does the same thing 
forever, even if supply power 
is repeatedly applied and 
removed. There are several 
ways this memory type can 
be taught. One is to use a 
factory programmed mask at 
the time of manufacture. 
Another is to use some field 
programming technique such 
as melting internal silicon or 
metallic fuses. This is handy 
whenever you are doing a 
special, low volume code or 
program, or whenever you 



Fig. 1. Read Only Memories 
(ROMs) are non-volatile and used 
typically for programming of 
"firm" microcomputer software, 
for fixed lookup tables, or for 
code conversions. 



INPUT 
WORD 
SELECT 





ROM 




. 
















' 




' 




* 









OUTPUT 
WORD 



OUTPUT 
ENABLE 



64 



aren't sure what you arc 
doing is really what you want 
to end up with. Such pro- 
grammable read only 
memories (PROMs) allow 
customizing for special pur- 
poses. Some of the more 
expensive programmable read 
only memories can be bulk- 
erased through exposure to 
ultraviolet light or X-rays; 
these erasable read only 
memories (EROMs) can be 
rc-programmed in the event 
of an error. 

Most read only memories 
can also be called code 
converters or table lookup 
devices, and are usually 
organized as shown in Fig. 1. 
Each ROM is a fixed logic 
block that has several inputs 
and several outputs. For each 
and every possible input 
address combination of ones 
and zeros, some unique 
combination of output ones 
and zeros will result. There 
doesn't have to be any 
rational relationship between 
these two code words. Either 
you or the manufacturer 
decides what these 
combinations are going to be 
at the time the ROM is 
programmed. A ROM is 
completely universal; it's 
inherently set up to provide 
all possible combinations of 
input /output word 
arrangements. When you 
program your ROM, you 
limit these all possible 
combinations to a single 
specific word exchange that 
you want. 

One popular smaller ROM 
arrangement is called a 32 x 8 
ROM. This means you can 
program 32 eight bit words. 
Since 32 words can be 
represented with binary 
combinations on five lines, 
this particular ROM has five 
input lines and eight output 
lines. This type of ROM has 
256 possible memory 
locations. At each and every 
location, we have the option 
of permanently or 
semi-permanently placing a 
one or a zero. This leaves us 
with 2^56 possible programs 
we can teach our ROM, an 



incredibly large number. The 
only thing that changes with 
a particular program is where 
you put the ones and zeros. 
All the rest of the circuit 
stays the same. 

ROMs work by decoding 
each and every possible input 
state into a onc-of-n code and 
then recombining certain 
selected combinations of 
decodings into output words 
using OR circuits. Which 
combinations you use picks 
what the output word is 
going to be. 

There are several ways to 
program a ROM. It can be 
done at the factory where 
metal jumpers are provided or 
omitted to the tune of holes 
or no holes in a mask. 
Factory programming is 
cheap but must be done with 
a high volume product that 
has one internal code that 
lots of users can agree to use. 
Dot matrix character 
generators, some keyboard 
encoders, trig lookup tables 
for calculators and so on are 
typical factory programmed 
ROMs. Field programmable 
ROMs are programmed by 
the user, or by a distributor 
or someone else who is set up 
to do programming. A 
programmable ROM arrives 
from the factory either all 
ones or all zeros, depending 
on the type. You then do 
something to change the bits 
you want to suit your code. 
In one type of ROM, fusable 
links are melted. These links 
are made of a metal such as 
nichromc, or of a 
semiconductor such as 
silicon. These techniques are 
most commonly used on 
bipolar or TTL-like ROMs. 
These ROMs are usually fast 
and relatively small. Another 
type of programming injects 
large voltage pulses that 
avalanche charge storage 
areas, electret style. This type 
of programming is used on 
MOS read only memories. 
They are usually slower but 
have more bits available per 
package. 

Some premium ROMs are 
reprogrammable. In one type, 



you take off an opaque lid 
and bulk erase the chip with 
strong ultraviolet light. A 
second type can have ones or 
zeros selectively and more or 
less permanently written into 
it. Reprogrammable ROMs 
cost more but can be used 
over. More important, if you 
make a programming mistake, 
you can reuse the same chip, 
correcting the error later on. 

We can also classify ROMs 
as general purpose devices 
and dedicated ones. A general 
purpose ROM can be made 
into whatever you like and 
used for just about anything, 
such as for code conversion, 
or to store programs for a 
microcomputer or 
microprocessor. Dedicated 
ROMs are usually part of a 
larger integrated circuit and 
have very specific uses. 
Typical examples are in a dot 
matrix character generator, 
the word converter in a 
premium keyboard encoder, 
and the program storage in 
many calculator integrated 
circuits. 

Let's see how ROMs work 
and what devices are available 
by looking at two important 



Fig. 2. Removing redundant 
information from the 7-segment 
calculator display code. 



"If you do a PROM 
design and end up with 
a ridiculous number of 
bits, you can almost 
always go through a 
rethinking and 
reduction process that 
will minimize things a 
bunch." 



(a) Segment callouts. 



(b) Numerals with segments 
"c" and "d" missing are still 
identifiable. 



m 

f b 

H 

e c 

LJ 



DUE 



i i 



DD 



i i 
i i 



65 



"Even with bulk erasable PROMs, a mistake on bit 
#1874 of a 2k PROM can be enough to ruin your whole 

day." 



Fig. 3. ROM-organized logic to convert 7segment calculator code to Fig. 4. Single IC 7 segment code converter uses 32 x 8 read only 
BCD or ASCII code. memory. 

(a) Circuit using 32 x 8 ROM. 



7- SEGMENT 
INPUTS 



4 LINE TO 

1/16 DECODERS 



4514 (CMOS) 



a o- 
b o- 



CO(NC) 
d O(NC) 

e o 

f o- 



I l 



go- 



in 



li'i 



LL_L 



/JTJ 

64 



• 7 7 V 7 -W 



IOOK 
TYP 



MO) 



• (3) 



J(2) 

so) 



50) 



(4) 



-•(6) 
1(8) 



32 16 6 4 

ASCII OR BCD OUTPUTS 



uses for ROMs — a seven bar 
to ASCII converter that can 
be used to tie a calculator 
into a TV typewriter or 
microcomputer; and an 
ASCII to SELECTRIC code 
converter that lets us drive a 
Selcctric typewriter. 

Seven Segment Converter 

Many calculator chips 
output only a seven segment 
code that is not directly 
compatible with 
microcomputer software 
unless it is changed to a 
Binary Coded Decimal (BCD) 
or ASCII coding. While 
several conversion ICs exist, 
at this writing, they are 
neither cheap nor readily 
available. Can we do the job 
with a read only memory? 

At first glance, it would 
seem that we'd need a ROM 
with seven inputs or 2 7 - 1 28 
words minimum. But, with 



practically every ROM 
application, a little bit of 
rethinking can usually 
drastically cut down the size 
and cost of the ROM we'll 
need. For instance, Fig. 2 
shows how we can simply 
ignore the bottom and 
bottom right segments ("c" 
and "d") of the segment code 
and still have ten distinct and 
identifiable characters. This 
cuts us down to 32 words, 
getting us by with five inputs, 
and one fourth the size of the 
ROM we started with. 

Fig. 3 shows us how we 
might build our own 
"pseudo-ROM" using some 
CMOS gates and decoders. 
While you would rarely want 
to go this route, it's useful to 
look at since it shows us how 
the real ROMs work inside. 
You might occasionally use a 
circuit like this to verify 
programs and truth tables 









8256 
ROM 
























I 

2 
4 
8 
16 




7 SEGMENT 






. 


INPUT 


~~° * OUTPUT 




d 
























— NC 

— NC 

— NC 


l_(j VALID 










KP 












a 1 







(b) Programming. 





INPUT 




NUMERAL 


g 


f 


e 


b 


a 



















— 














1 


- 











1 





1 











1 


1 


7 








1 








— 








1 





1 


- 








1 


1 





- 








1 


1 


1 


- 





1 

















1 








1 


- 





1 





1 





- 





1 





1 


1 


- 





1 


1 








_ 





1 


1 





1 


- 





1 


1 


1 





— 





1 


1 


1 


1 





1 














_ 


1 











1 


— 


1 








1 





- 


1 








1 


1 


3 


1 





1 








_ 


1 





1 





1 


- 


1 





1 


1 





- 


1 





1 


1 


1 


2 


1 


1 











_ 


1 


1 








1 


5 


1 


1 





1 





4 


1 


1 





1 


1 


9 


1 


1 


1 








— 


1 


1 


1 





1 


6 


1 


1 


1 


1 





- 


1 


1 


1 


1 


1 


8 



OUTPUT 

kp 8 4 2 1 





10 1 

10 111 























10 







10 11 







10 10 



10 10 1 

10 10 

110 1 



10 110 



110 



66 



since it is easy to change. 

Our five input lines 
(ignoring the redundant c and 
d segments) are decoded to a 
one-high-out-of-32 code. For 
each and every possible input 
combination, one and only 
one of the horizontal rails 
goes to a "1"; the rest stay 
low. The OR gates on the 
output re-encode this into a 
1-2-4-8 Binary Coded 
Decimal code. We decide 
what our OR gates do by 
where we put the dot 
connections between the 
horizontal and vertical rails. 
To get from BCD to ASCII, 
we can simply tack a hard 
wired 01 1 in front of the 
BCD word. 

While we could dream up a 
possibly simpler "logical 
minimum" circuit to do the 
same job, this particular 
circuit has a unique advantage 
- if our OR gates are "wide" 
enough, it will convert ANY 
five bit input word into ANY 
four bit output word, with no 
change in hardware. All that 
changes is the positions of the 
dots. This is the beauty of the 
read only memory — only a 
single integrated circuit is 
needed to do an incredible 
variety of specialized jobs, 
depending only on how you 
program it. 

Fig. 4 shows how we take 
a stock 32 x 8, 256 bit 
Programmable Read Only 
Memory, or PROM, and do 
the whole job with one 
integrated circuit. Since we 
have extra outputs left over, 
we can use one for a "valid 
keypressed" output that can 
tell the difference between a 
zero code and no key pressed. 
The remaining three outputs 
can be used for detecting a 
"9" output or for other 
housekeeping that's handy 
when you demultiplex the 
scanning digit outputs of the 
calculator IC. To program the 
ROM, the truth table of Fig. 
4(b) is entered into the 
integrated circuit, selectively 
putting ones and zeros as 
needed. 



MANUFACTURER 


PART 


HITS 


ORG. 


TYPE 


ERASABLE? 


AMERICAN MICRO DEVICES 


27S08, 09 


256 


32x8 


BIPOLAR 


NO 




27S10, 11 


1024 


256x4 


BIPOLAR 


NO 




1702 


2048 


256x8 


MOS 


YES 


HARRIS SEMICONDUCTOR 


1256 


256 


256x1 


BIPOLAR 


NO 




8256 


256 


32x8 


BIPOLAR 


NO 




0512 


512 


64x8 


BIPOLAR 


NO 




1024 


1024 


256x4 


BIPOLAR 


NO 




2048 


2048 


512x4 


BIPOLAR 


NO 


FAIRCHILD 


93421 


256 


32x8 


BIPOLAR 


NO 




93416,26 


1024 


256x4 


BIPOLAR 


NO 




93436,46 


2048 


512x4 


BIPOLAR 


NO 


INTEL 


3601 


1024 


256x4 


BIPOLAR 


NO 




3602,22 


2048 


512x4 


BIPOLAR 


NO 




1702 


2048 


256x8 


MOS 


YES 




3604.24 


4096 


512x8 


BIPOLAR 


NO 




2704 


4096 


512x8 


MOS 


YES 




2708 


8192 


1024x8 


MOS 


YES 


INTERSIL 


5600,10 


256 


32x8 


BIPOLAR 


NO 




5603,23 


1024 


256x4 


BIPOLAR 


NO 




5604,24 


2048 


256x8 


BIPOLAR 


NO 


MONOLITHIC MEMORIES 


6330,31 


256 


32x8 


BIPOLAR 


NO 




6300,01 


1024 


256x4 


BIPOLAR 


NO 




6305,06 


2048 


512x4 


BIPOLAR 


NO 




6340,41 


4096 


512x8 


BIPOLAR 


NO 


NATIONAL 


8573,74 


1024 


256x4 


BIPOLAR 


NO 




5202,03 


2048 


256x8 


MOS 


YES 




5204 


4096 


512x8 


MOS 


YES 


NITRON 


7002 


1024 


512x2 


MOS 


YES 




7002 


1024 


1024x1 


MOS 


YES 


SIGNETICS 


8223 


256 


32x8 


BIPOLAR 


NO 




82126,29 


1024 


256x4 


BIPOLAR 


NO 




82130,31 


2048 


256x8 


BIPOLAR 


NO 




82115 


4096 


512x8 


BIPOLAR 


NO 


TEXAS INSTRUMENTS 


74188 


256 


32x8 


BIPOLAR 


NO 




74186 


512 


64x8 


BIPOLAR 


NO 




74287 


1024 


256x4 


BIPOLAR 


NO 



Fig. 5. Some commercially available programmable ROMs. 



Working With PROMs 

Fig. 5 is a listing of some 
currently available PROMs. 
Where two numbers are 
shown, one is usually an open 
collector output, the other 
tri-state. At this writing, 
PROMs cost from $5 
upwards, with surplus 
versions (unused) starting 
at $3. Bipolar PROMs are 
based on a TTL technology, 
usually work off a single +5 
volt supply, and are rather 
fast, typically 50 to 70 
nanoseconds access time. 
MOS PROMs often take two 
power supplies (+5 and —12 
usually) and are slower, 
typically having a one 
microsecond access time. 
MOS PROMs are often 
cheaper per bit and many 
MOS types are bulk erasable 
by exposure to strong ultra- 
violet light. A few ultra-fast 
ECL PROMs also exist, but 
are reserved for special uses 
and are expensive. 

Two good choices for 
home brew computing are the 
32 x 8 bipolar PROM such as 
the Intersil 5600 or the 
Signetics 8223; and the 256 x 



8 erasable MOS PROM, 
including the Intel 1702 and 
its second sources. 

While you can program 
your own PROM with 
nothing but a power supply 
and a meter, the "zero 
defects" nature of this work 
and its "up the wall" aspects 
turn the job into quite a 
hassle. Even with bulk 
erasable PROMs, a mistake on 
bit #1874 of a 2k PROM can 
be enough to ruin your whole 
day. Instead of this, you can 
buy programming services at 
very low cost from many 
electronic distributors, as well 
as from surplus and computer 
hobby supply houses. 
Programming machines that 
simplify the job a bunch are 
available for several hundred 
dollars. [Once you have a 
microcomputer system up 
and running, it is quite 
possible to construct an ROM 
programming peripheral for 
the purpose of permanently 
burning in your software. 
Local computer clubs might 
consider building the ROM 
burner peripheral and related 
software as an attraction of 
membership . . .cth] 



A quarter's worth of 
gating can cut the size 
of a ROM in half. 



When you design your 
own PROM circuit, be 
absolutely sure your truth 
table is correct before you 
order any programming. The 
program service will only 
guarantee that what you sent 
in is what you get back, and 
nothing more. They have no 
way of second guessing what 
you really wanted. 

If you do a PROM design 
and end up with a ridiculous 
number of bits, you can 
almost always go through a 
rethinking and reduction 
process that will minimize 
things a bunch. Leaving off 
the two redundant segments 
of a seven bar code is one 
obvious example. Other 
possibilities are to put simple 
logic outside the PROM, for 



67 



Fig. 6. ASCII to SELECTR1C interface using PROM. 



ASCII 
INPUTS 

al 



a2 O 




O ROTATE I 

"T— O ROTATE 2 
O ROTATE 2A 



BALL 
O ROTATE 5 ) OUTPUTS 



— O TILT 2 
HIFT 



1 O SHI 



D- 



-tO 



KP TO SPACE 



KP TO RETURN 



NOR l_i ^ 



_o KP TO PRINT 
SOLENOID 



BALL SOLENOIDS 



often a gate or two can 
significantly reduce the 
PROM size. Bypassing control 
commands around a PROM is 
one way to do this. 
Sometimes symmetry and 
mirror techniques can be 
used, particularly when 
working with trig waveforms, 
music waveshapes, and other 
data tables that have some 
sort of symmetry. In PROM 
microcomputer programs, 
sneaky programming tricks 
can often drastically cut the 
number of steps needed; 
extensive use of subroutines 
is one route to this end. 

In code converter and 
table lookup applications you 
usually address your PROM 
in a random fashion and you 
have no way of knowing what 
is going to be needed next. 
There are other ways to 
address ROMs that open up 
other types of applications. 
For instance, if you 
sequentially clock the PROM, 
changing the address one bit 
at a time at a constant rate, 
you can generate an output 
sinewave or a musical timbre 
waveform. The clocking rate 
will select the output 
frequency, and you can get a 
symmetrical output by using 



an up down counter driving 
the address inputs. Another 
possibility is to let the 
PROM's output set the next 
input address to the PROM, 
or at least influence it. Some 
outside latch or storage is 
needed to prevent an 
unchecked wild race, but this 
is easily added. 

This particular technique 
is called microprogramming, 
and is, of course, the key to 
calculator and micro- 
computer operation. Even 
without a CPU, a PROM plus 
additional logic can be used 
as a programmable controller. 
Loops and branches are easily 
added by external gating and 
using extra PROM inputs. 
Several additional details on 
PROM and ROM design 
appeared in the February, 
1974, Radio Electronics. 

A ROM or PROM can be 
used to change ASCII coded 



signals into SELECTRIC 
outputs suitable for the hard 
copy techniques output if 
you have a converted 
Selectric typewriter. While a 
few ICs are commercially 
available to do this job (such 
as the Fairchild 3512 and the 
National 4230), at this 
writing, it's much cheaper 
and simpler to program your 
own PROM. You can also add 
custom features of your own, 
such as converting the ASCII 

^ command into a capital 
"E" and so on. 

Fig. 6 shows us a circuit 
that only needs 512 bits 
worth of ROM and a few 
gates to do the one-way 
conversion for us. The PROM 
basically works with the 
ASCII 6 bit code of upper 
case alphabets, numbers and 
punctuation. It converts these 
ASCII commands into the 
seven Selectric shift, rotate 



Fig. 7. Listing of ASCII inputs (octal) and Selectric outputs for the PROMs in Fig. 6. 



ASCII 




SELECTRIC 


ASCII 






SELECTRIC 


INPUT 


CHARACTER 


OUTPUT 


INPUT 


CHARACTER 


OUTPUT 


100 


ca 


166 




040 


SPACE 




200 


101 


A 


134 




041 




I 




177 


102 


a 


140 




042 








125 


103 


c 


154 




043 




# 




176 


104 


D 


155 




044 




S 




171 


105 


E 


145 




045 




% 




135 


106 


F 


116 




046 




& 




175 


107 


G 


117 




047 








025 


110 
111 
112 

113 
114 


H 
I 

J 
K 
L 


141 
124 
107 
144 
151 




050 
051 
052 
053 
054 




( 
) 




160 
161 
174 
106 


115 
116 
117 


M 

N 



137 
146 
131 




055 
056 
057 




/ 




000 
026 
011 


120 


P 


105 




060 









061 


121 


Q 


104 




061 




1 




077 


122 


R 


135 




062 




2 




066 


123 


S 


121 




063 




3 




076 


124 


T 


147 




064 




4 




071 


125 


U 


156 




065 




5 




065 


126 


V 


136 




066 




6 




064 


127 


W 


120 




067 




7 




075 


130 


X 


157 




070 




8 




074 


131 


Y 


101 




071 




9 




060 


132 


Z 


167 




072 








115 


133 


I 


111 




073 








015 


134 


\ 


1S4 




074 




< 




027 


135 


I 


111 




075 




= 




006 


136 


A 


145 




076 




> 




127 


137 


ASCII 


100 




077 
SELECTRIC 




? 




111 

READING 


6 


5 4 3 2 1 




SPSH 


T2T1 R5 R2A R2 Rl 




BITS 


OCTAL 


0_ 


1 0, 1 \ 


U 


1 


,1 1, 


1 




BINARY 






2 5 


U 


1 


5 


6 




OCTAL 





68 



and tilt ball commands. The 
program appears in Fig. 7. 
We've shown it in octal 
coding to make it more 
compact. 

Most of the characters are 
directly converted from 
ASCII to their SELECTRIC 
equivalents. ASCII < and > 
become the Selectric 1/2 and 
1/4 respectively, the ASCII 
\ becomes the Selectric i, 
and opening and closing 
brackets are disallowed and 
produce question marks. 
ASCII { becomes a 

capital "E" to indicate 
exponentiation, particularly 
when using the BASIC 
language on a microcomputer 
output display. 

The eighth output of our 
PROM is used to detect an 
ASCII space and break it out 
of the code, for a Selectric 
space is a machine command, 
and an ASCII space is a 
printing character. If a space 
is detected, the keypressed 
output is diverted to the 
space solenoid and the ball 
moving solenoids are 
disabled. 

If a lower case alphabet is 
provided, the input logic on 
bits a6 and a7 detects lower 
case and converts it to its 
equivalent upper case ASCII 
six bit input code and at the 
same time forces the shift 
output line to the lower case 
low state. This is a good 
example of how a quarter's 
worth of gating can cut the 
size of a ROM in half. 

Another Selectric machine 
command we need is a return 
command to move the ball 
back to the beginning of a 
line. This command can be 
detected with the lower left 
NOR gate (Fig. 6) and used 
to divert the keypressed 
output to the carriage return 
solenoid, at the same time 
disabling the ball-moving 
solenoids. If there should be 
any other control commands 
which are to be ignored by 
the typewriter, carriage 
return detection logic 
(OPTIONAL CR GATING in 
Fig. 6) can be added to 
distinguish carriage returns 



Fig. 8. Full function ASCII to SELECTRIC code converter uses larger 
PROM. 



ASCII 
INPUT 




O ROTATE I 
O ROTATE 2 
O ROTATE 2A 
O ROTATE 5 
O TILT I 

TILT 2 

SHIFT j 

SPACE 

RETURN 

INDEX 

TAB 

BACKSPACE 

BELL 

SPARE 



BALL 
) OUTPUTS 



\ MACHINE 
' OUTPUTS 



GOES TO "I" ON PRINTABLE CHARACTER; - 
"0" ON MACHINE COMMAND 



KP TO PRINT 

SOLENOID 

KP TO MACHINE 

SOLENOIDS 

BALL SOLENOIDS 
ENABLE 



from the added control 
commands. 

You can build this ASCII 
to Selectric interface using a 
single 64 x 8 PROM or a pair 
of 32 x 8 PROMs with 
parallel outputs selected by 
the chip enable inputs. Using 
two ICs is sometimes less 
expensive than one larger 
PROM because the smaller 
PROMs are more widely 
available as surplus. Fig. 5 
lists several typical PROM 
parts. 

All Selectric functions 
including bell, tab, backspace 
and index are accommodated 
in the circuit of Fig. 8. It 
takes a PROM of four times 
the size, provides more 
functions, and is a simpler 
circuit than the one shown in 
Fig. 6. The eighth PROM 
output is used to decide 
whether the ASCII code is a 
printed character or a 
machine command (which 
might be ignored). This 
eighth output line feeds back 
to the PROM's eighth input 
line via the resistor-capacitor 
time delay circuit. When bits 
1 to 7 of the PROM input 
represent a printable 
character, the eighth bit 
output line switches to a high 



level which enables printing. 

The ball output codes are 
the same as in the simpler 
circuit, but their solenoids 
must be disabled when the 
machine command codes are 
received. When a character is 
to be printed, the keypressed 
pulse (KP in Fig. 8) is routed 
by the upper AND gate 
(enabled by the logical one 
output of the PROM's eighth 
bit) to the print solenoids; 
the ball solenoid enable is 
also taken from the eighth 
PROM bit. The result is 
movement of the ball 
combined with a print stroke. 

If, however, a machine 
command is presented to the 
PROM at the ASCII inputs, 
the eighth bit of the PROM 
output goes low and disables 
both the ball solenoids and 
the gate which would route 
KP to the print solenoid. This 
bit is inverted by the inverter 
to present a logical one level 
to the lower AND gate in the 
figure. This enables the 
keypressed pulse (KP) to go 
to the machine solenoids. 
Any legitimate command 
code will result in selection of 
one of the machine outputs 
in Fig. 8 . The 
selected machine output line 



will enable the corresponding 
machine control solenoid's 
driver — resulting in one of 
the machine control actions 
such as a tab. As an example, 
suppose a horizontal tab 
function (HT in ASCII) is 
presented to the PROM: The 
PROM decodes a machine 
command, inhibits ball 
solenoids and the print 
solenoid, presents a decoded 
logical one level to the tab 
solenoid driver, enabling it, 
and routes the keypressed 
signal (KP) to the other tab 
solenoid driver input — 
resulting in a tab action. 
Since the PROM is to be set 
up for only six (or seven) 
legitimate machine 
commands, any unwanted 
ASCII machine control codes 
will be ignored. 

In this article, we've seen 
some background 
information on ROM 
technology and several of the 
many uses to which ROMs 
can be put in microcomputer 
and logic systems. These are 
by no means the only uses of 
ROMs. The uses of ROM 
technology are for the most 
part limited only by your 
own imagination. ■ 




' 



THE HP 65: WORLD'S 
SMALLEST COMPUTER SYSTEM 



by 

Richard Nelson 
HP-65 Users Club 
2541 W. Camden PI. 
Santa Ana CA 92704 



On Jan. 17, 1974, 
Hewlett-Packard announced 
their fourth model in a 
continuing series of 
sophisticated pocket 
calculators. This model, the 
HP-65, was unique in that it 
was programmable and used 
magnetic cards to read and 
write user-written programs. 
One of the first questions 
asked about the new machine 
was, "Is it a calculator or a 



computer?" There is no 
question that the HP-65 is the 
most powerful computational 
tool in existence for its size 
and weight, but in terms of 
an Altair 8800, Mark I or 
Sphere microcomputer, how 
does the HP-65 stack up? 

Computer vs. Calculator 

In the classical definition 
of a computer, as described 
by Babbage, the HP-65 is 



indeed a computer. The 
HP-65 has conditional and 
unconditional branching, data 
storage, and a memory which 
can be used to store a 
program. By today's 
standards a machine is often 
called a computer or a 
calculator by the task for 
which it is best suited. A 
calculator is best suited for 
numerical calculations, and a 
computer is best suited for 



70 



binary or alphabetic data 
manipulations involving a 
large data base. In this sense, 
the HP-65 is - as it is called 
— a calculator. 

If you are interested in 
computers and programming, 
should you consider the 
HP-65? Most definitely! The 
only negative aspect of the 
HP-65, compared to atypical 
microcomputer kit, is its cost 
(i.e., $795 versus about 
$500). If, however, you 
consider the microcomputer 
complete with an operating 
system and an input/output 
device — but built into a 
pocket-size package, then the 
HP-65 is a very competitively 
priced unit. 

There is no doubt that the 
HP-65 "computer" is the 
easiest to get up and running. 
If your interests are primarily 
of a problem-solving nature, 
and a personal, portable 
computational and 
educational tool will meet 
your needs, the HP-65 is for 
you. 

If your interests tend 
toward programming, the 
HP-65 is an excellent machine 
to learn programming upon. 
If you master memory 
limited (every computer is 
memory limited sooner or 
later) programming on the 
HP-65, you will have an 
excellent background to 
move up to a larger machine 
if you desire. There will be no 
problem selling a used HP-65. 
Just try buying one! 

How Powerful is the HP-65? 

The HP-65 has 100 
memory steps, and 14 data 
registers (four in the stack) 
directly accessible to the user. 
Programs may be linked from 
card to card if efficient 
programming won't allow 
placing all steps on one card. 
Card read time is about the 
same as the dial "0" time on 
an older model telephone. 
Four logical comparison 
operations, two flags, 
decrement counter, 
convenient editing, five 
user-defined keys and merged 
codes which allow two 



keystrokes to occupy only 
one step of memory all 
combine to make the HP-65 
so powerful that it was used 
to backup the on-board 
computer on later Apollo 
missions. Programs have been 
written for the HP-65 to 
perform some amazing 
calculations — and other tasks 
as well. 

Hewlett-Packard has 
nearly 4,000 programs in 
their library, all available to 
HP-65 users. A catalog details 
and classifies each program. 
Hewlett-Packard also offers 
collections of programs in the 
form of PACs containing 40 
pre-recorded cards. To date, 
14 PACs are available, 
covering the fields of finance, 
mathematics, electrical, 
chemical and mechanical 
engineering, medicine, 
surveying, aviation and 
navigation. 

The HP-65 can be 
programmed to: 

a) Play Tic-tac-toe, N1M, 
Bagels, Craps, Ping-pong, 
Slot Machine, Football or 
Hexapawn. Some games are 
cybernetic — one card — 



and will actually learn to 
play a perfect game. 

b) Generate 10,000 digits 
to test a random number 
routine, sort and tally the 
digits 0-9 to check the 
routine's uniformity. 

c) Play word games such 
as Word Squares or 
Hangman. 

d) Generate a table of 
prime numbers. 

e) Solve up to seven 
simultaneous equations in 
seven unknowns. 

f) Design a transistor 
amplifier circuit with all 
calculated values converted 
to El A standard values. 

g) Teach students 
arithmetic using teaching 
programs that adjust to the 
learning rate of the student. 

h) Compute double 
precision products such as: 

9, 753, 124, 680 

x9, 375, 168,024 = 

91,437,182,634, 

021,232,320 

(64-bit arithmetic is not 
enough precision for this 
number-crunching 
application.) The latter is an 



example of the type of 

problems in which the 

calculator is outstanding 

and the microcomputer is 

marginal. Try an alphabetic 

sort of the names of the 

members of your car pool 

and the situation is reversed. 

Like all e lectronic 

''computers," someone 

always applies their machine 

in unusual ways in an attempt 

to solve a problem. For blind 

users a program has been 

written for the HP-65 which 

will produce a tone on a radio 

in the form of coded beeps to 

"spell out" the display. One 

user has applied a program to 

generate points to plot a 

modern art figure. In the 

search of trying to get 200 

steps into a 1 00-step 

memory, users have even 

found logic that wasn't 

intended to be included in 

the instruction set. Many 

HP-65 users get the most 

from their machine by 

sharing their experiences 

through an organization 

established for that purpose. 

Most computers have users 

groups — for the HP-65 it is 

the HP-65 Users Club. ■ 




71 



Build A 6S00 System 
With This Kit 



by 

Gary Kay 

Southwest Technical Products Corp. 

21 9 W. Rhapsody 

San Antonio TX 78216 



If you are one of the many 
people getting ready to 
purchase one of the 
reasonably priced 
microprocessor system kits 
on the market today, you 
might ask yourself whether or 
not you will be able to start 
entering programs once you 
get it all put together. Of 
course you can always load 
programs and data through 
the front panel programmer's 
console, but most individuals 
aware of the front panel's 
slow speed and difficult 
readability prefer to use a 



Teletype or low cost video 
terminal such as the TV 
Typewriter II (February 1975, 
Radio Electronics) for data 
and program input/output. 
This is all well and good 
except that in order to attach 
a terminal, you'll have to 
purchase an interface for 
your computer if it is not 
supplied with the basic 
system. In fact you will 
generally need a separate 
interface for each I/O 
(input/output) device 
connected to your computer. 
This can run your system 



investment up considerably 
since such interfaces typically 
cost between $75 and $150 
each, and there are more 
surprises yet to come. 

So now you've got your 
computer, with interface, 
attached to your terminal; 
you're ready to sit down, 
power up and start typing in 
your program, right? Well, 
not quite. You see, in order 
to be able to use the terminal 
for either entering programs 
or getting data in and out of 
the computer you must have 
a program resident or loaded 



Fig. J. Block diagram of the SWTPC 6800 system. The address allocations of the elements of the system are 
noted inside the blocks. 




into memory telling the 
processor how and what to 
do. Without this software 
(program), you can pound on 
the keyboard all you want 
and the computer won't do 
anything. Computers are no 
smarter than their 
programming lets them be 
and without programming 
they're not very smart at all. 
How do you get this software 
into memory? Well, you 
could load it in from paper or 
cassette tape, that is if you 
have a paper tape reader or 
cassette tape interface 
(another sizable investment) 
or you could enter it directly 
from the programmer's 
console. The problem here is 
two fold. Software to give the 
terminal reasonable system 
control will probably be 
around 500 words in length. 
This is far too long to enter 
from the programmer's 
console especially when you 
consider it has to be 
re-entered every time the 
system is powered up or after 
a wayward program 
overwrites any of its allocated 
area of memory. The second 
problem is that few if any of 
the manufacturers supply a 
listing, paper tape or cassette 
tape of such a program to 
begin with. Their terminal 
control routines are 
contained within 
editor/assembler and higher 



72 



MEMORY BOARD 



CONTROL INTERFACE 



CPU BOARD — i 



MOTHERBOARD 




MCM6810L1 
128X8 RAM 



POWER 
SUPPLY 



MCM6830L 

"MIKBUG" 

ROM 



MC6800 
PROCESSOR 



Details of the SWTPC 
6800 System. This photo 
illustrates what you see 
when you remove the 
cover of a typical SWTPC 
computer system. This is 
an assembly of the parts 
which come in the MP-68 
kit. 



level language packages which 
not only must be loaded from 
some kind of tape reader, but 
require from 4,096 to 8,192 
words of memory to operate. 
And you thought the 
interfaces were expensive, 
just check the prices on 8,1 92 
words of memory. Many of 
the systems now on the 
market are supplied with an 
amount of memory with the 
basic unit which is 
considerably less than what 
might actually be needed for 
useful programming. 

So what's the alternative? 
Well, the system presented in 
this article has been designed 
to eliminate the afore- 
mentioned problems and 
allow the user to have a 
powerful and fully functional 
system at a minimum cost 
(see Fig. 1). The entire 
system is built around the 
Motorola MC6800 
microprocessor and its family 
of support devices. The 
computer itself is being made 
available in kit form including 
the chassis, cover, power 
supply and all circuit boards, 



parts and hardware necessary 
to build a Motorola 6800 
based microprocessor 
including a 1,024 word ROM 
(read only memory) stored 
operating system with 
1 2 8- word scratch pad 
memory, serial interface baud 
rate generator, serial 
interface, and 2,048 words of 
memory for $450. This 
article gives a description of 
the microprocessor and 
mother board. A future 
article will describe the power 
supply, memory and interface 
boards. 

The Microprocessor/System 
Board (MP-A) 

The Microprocessor/ 
System Board (coded MP-A) 
is the primary logic board for 
the system. It is a 5 1 /2" x 9" 
double sided plated-through 
hole circuit board containing 
the 6800 microprocessor 
chip, the 6830 ROM which 
stores the mini-operating 
system and the 6810, 
1 28-word scratch pad random 
access memory (RAM) 
needed by the ROM. 



There is a crystal controlled 
processor clock driver and 
baud rate generator providing 
serial interface baud rates of 
110, 150, 300, 600 and 1200 
baud for all but the terminal 
control interface which is 
operable at 110 or 300 baud. 
Also provided is a power 
up/manual reset circuit which 
restarts the ROM stored 
mini-operating system 
whenever activated. Full I/O 
buffering is provided for the 
16 address lines and eight 
bidirectional data lines with 
these and other connections 
made to the rest of the 
system through the mother 
board via a 50-pin connector. 
Power for the board is 
derived from a +5 volt 
regulator fed from the 
system's unregulated 7 volt, 
10 Amp power supply. 
Average current consumption 
for the board is 0.8 Amps. 

The mini-operating system 
stored in the 6830 ROM on 
this board has got to be one 
of the most outstanding 
features of this system. It is 
through this Motorola written 



software package called 
"MIKBUG" that the user can 
1) enter program or data into 
memory from either the 
terminal's keyboard or tape 
(where applicable), 2) jump 
to and execute a program 
loaded in memory, 3) list 
programs or data stored in 
memory, on the terminal or 
tape (where applicable), 4) 
examine and/or change the 
contents of the internal CPU 
registers, 5) examine and/or 
change the contents of 
specified memory locations. 
These operations are 
performed using a 20 mA 
current loop Teletype or an 
RS-232C compatible serial 
ASCII terminal. 

This ROM mini-operating 
system does not have to be 
loaded from tape and it 
cannot be overwritten. It is 
always there at your 
fingertips — just pressing the 
RESET button or simply 
powering the system up 
automatically restarts this 
firmware (ROM stored 
software). When activated, 
this system responds with a 



73 



r 



i ffff 



MINIBUG/ 

TEST PATTERN 

(NOT USED) 



MIKBUG 
ROM 



MIKBUG 
RAM 



I/O PORT 
N0.7 



I/O PORT 
NO. 6 



I/O PORT 
NO.5 



I/O PORT 
NO. 4 



I/O PORT 
NO. 3 



I/O PORT 
NO. 2 



I/O PORT 
NO.I CONTRL. 
INTERFACE 



I/O PORT 
NO.O 



4K MEMORY 
NO. 7 



4K MEMORY 
NO. 6 



4K MEMORY 
NO.5 



4K MEMORY 
NO. 4 



4K MEMORY 
NO. 3 



4K MEMORY 
NO. 2 



4K MEMORY 
NO. I 



4K MEMORY 
NO. 



EIFF 



EOOO 



A07F 



AOOO 



80IF 

801 C 
80IB 

8018 
8017 

8014 
8013 

8010 
800F 

800C 
800B 

8008 
8007 

8004 
8003 

8000 
7FFF 

7000 
6FFF 

6000 
5FFF 

5000 
4FFF 

4000 
3FFF 

3000 
2FFF 

2000 
IFFF 

1000 
OFFF 
0000 



Fig . 2 . SWTPC 68 00 
Microprocessor System memory 
map. The 64K address space of a 
6800 CPU is divided up into the 
segments shown here. The first 
32K locations are available for 
user read-write memory. The 
second 32K is devoted to I/O port 
assignments and the requirements 
of the MIKBUG program supplied 
by Motorola. 



carriage return, line feed and 
then prints a * on the 
terminal at which time you 
may enter various single 
character control commands 
such as M for memory 
examine/change, L for load 
from tape, P for punch or list, 
R for examine registers or G 
for go to and execute a 
loaded program. A program 
debug routine can also be 
implemented by using the 
software interrupt (SWI) 
instruction as a "breakpoint" 
which forces a jump from 
your program to the 
operating system to allow 
you to examine the contents 
of memory and/or the CPU 
registers. All data entered or 
displayed through the 
terminal is in convenient 
hexadecimal (base 16) 
notation. This means you can 
type in a command to load 
address location AOOO16 with 
9E-|5 instead of setting 24 
console switches to an 
address of 1010 0000 0000 
0000 with data of 1001 1110 
as must be done with the 
conventional programmer's 
console. Since the operating 
system is stored in ROM, it 
consumes no user RAM 
memory, in fact, it actually 
gives the user a little extra. 
There is a 128-word scratch 
pad memory utilized by the 
operating system for storing 
various addresses and data, 
but there are more than 54 
locations within this 6810 
RAM memory which are 
totally unassigned plus a 
46-word deep push-down 
stack. All of this memory is 
in addition to the 2,048 
words (expandable to 4,096 
words) contained on the 
standard memory board. 

Since the terminal and 
mini-operating system 
provide the user with 
complete system control, 
there is no need for the 
conventional programmer's 
console. Take note also that 
once system control is turned 
over to your program, the 
control terminal is totally 
available for your program 



input/output. In fact, since 
the character input/output 
subroutines are already stored 
within the operating system 
ROM, they can be used by 
your programs simply by 
loading or storing the 
characters to be handled in 
the proper register and 
executing a jump to 
subroutine (JSR). 

The Motorola MC6800 
microprocessor chip is the 
element around which this 
entire system is built. It is an 
8-bit parallel processor with 
eight bidirectional data lines 
and 16 address lines giving it 
an addressing capability of up 
to 65,536 words. There is no 
distinction between memory 
and I/O addressing on this 
system, therefore, all 
input/output data transfers 
are handled just as are the 
memory transfers. This means 
the I/O interfaces must have 
their own allocated memory 
addresses where neither ROM 
or RAM memory may be 
located. This may at first 
seem to be a disadvantage 
until you realize that all 
memory handling instructions 
are usable for the interface 
data handling as well, thus 
eliminating the need for 
special data I/O instructions. 
The memory assignments for 
this system have to be made 
as shown in Fig. 2. User RAM 
may be located anywhere in 
the lower 32K (0000] 6 to 
8000-] 5) addresses with the 
upper 32K addresses reserved 
for the operating system 
ROM, RAM and interface 
boards. 

There are six registers 
internal to the MC6800 
microprocessor element 
which consist of the program 
counter, stack pointer, index 
register, accumulator A, 
accumulator B and condition 
code register. The stack 
pointer is a 16-bit register 
used to store the address of 
the push-down stack which is 
located in RAM memory 
external to the MC6800 
microprocessor element. The 
push-down stack itself is used 



to store the program counter 
and/or processor data during 
branch to subroutine (BSR), 
jump to subroutine ()SR), 
push (PHS) or interrupt 
routines. The index register is 
a 16-bit register generally 
used as an address pointer for 
many processor instructions. 
There are 72 basic 
instructions for the 6800 
microprocessor system (Fig. 
3) with most of the 72 
utilizing several of the seven 
possible addressing modes: 
Accumulator, implied, 
relative, direct, immediate, 
extended and indexed. 

• Accumulator — In 
accumulator addressing, 
either accumulator A or 
accumulator B must be 
specified. 

• Implied — In implied 
addressing the instruction 
code itself specifies the 
operand (stack pointer, 
index register, etc.). 

• Relative — Relative 
addressing is used for the 
branch instructions and 
indicates the value 
contained in the word of 
memory immediately 
following the instruction 
code added to the program 
counter +2 with the result 
then loaded back into the 
program counter. Positive 
data (bit 7 = 0) generates 
forward jumps up to 129 
words from the branch 
instruction while negative 
data (bit 7 = 1) generates 
backward jumps up to 125 
words from the branch 
instruction. 

• Direct — In direct 
addressing, the value 
contained in the word of 
memory immediately 
following instruction code is 
an actual memory address 
within the first 256 words 
of memory (0000-] 6 to 
OOFF) which contains the 
operand of the instruction. 
This mode typically saves 
one CPU cycle of execution 
when compared to extended 
addressing. 

• I m m ediate — In 
immediate addressing, the 



74 



value contained in the word, 
or in some cases two words 
of memory, immediately 
following the instruction 
code is the operand of the 
instruction. 

• Extended — In 
extended addressing, the 
two words of memory 
immediately following the 
instruction code contain the 
address of the memory 
location which contains the 
operand of the instruction. 

• Indexed — In indexed 
addressing, the value 
contained in the word of 
memory, immediately 
following the instruction 
code, is temporarily added 
to the contents of the index 
register generating a new 
address where the operand 
of the instruction is located. 
The jump is positive only, 
going from to 255 words 
and the actual contents of 
the index register are not 
changed. 

Also provided on the main 
processor board is an 
MCI 4411 baud rate generator 
which uses an external 
1.8432 MHz crystal and 
internal oscillator and divide 
chain to generate serial 
interface clocks for baud 
rates of 110, 150, 300, 600 
and 1200 baud. Also derived 
from this circuit is the 921.6 
kHz clock used by the 
MC6800 microprocessor 
clement. It is first, however, 
fed into a gating circuit 
generating two non- 
overlapping, 50% duty cycle, 
complementary clock signals 
§] and §2- 

Mother Board (MP-B) 

The Mother Board (coded 
MP-B) is a 9" x 14" double 
sided, plated-through hole 
circuit board onto which all 
of the various processor 
boards are plugged. Provisions 
have been made for one 
Mi crop rocessor/ System 
Board, up to four 4,096 word 
random access memory 
boards plus two unused slots. 
This allows the system to be 
expanded to 16,384 words of 



memory. For those 
demanding even more 
memory, the 50-line system 
information bus may be 
paralleled onto another 
mother board with separate 
power supply expanding the 
system to a maximum of 
32,768 words of random 
access memory. 

The Mother Board also 
provides the line buffering 
and address decoding for up 
to eight interface boards. 
Although one of the eight 
must be the serial terminal, 
control interface, the other 
seven may be any 
combination of parallel or 
serial interfaces the user may 
choose to have. For those 
demanding even more 
interfacing capability, the 
50-line system information 
bus may be paralleled onto 
another mother Txiard with 
separate power supply 
expanding the interfacing 
capability to one terminal, 
control interface plus any 
combination of up to 15 
serial or parallel interfaces. 

The following is a brief 
description of each of the 50 
lines on the system 
information bus: 

The A0 - A15 lines 
carry address bits through 
15 respectively, forming a 
16-bit address which is used 
to define either a memory 
location or interface 
address. 

The BUS AVAILABLE 
line goes high ac- 
knowledging a processor 
halt, meaning the processor 
has stopped and that the 
system information bus is 
available for external 
control. 

The DO — D7 lines carry 
inverted data bits through 
7 respectively, forming 8-bit 
data words which are 
exchanged between the 
various boards within the 
system. 

The GND line is the 
system's common power 
supply ground point. 



Fig. 3. The 6800 microprocessor 's instruction set. This is a list of the 
mnemonics available. A more complete explanation of the basic 
operations of the processor is found in Motorola's programming manual 
for the 6800 which is part of the SWTPC documentation package. 



ABA Add Accumulators 

ADC Add with Carry 

ADD Add 

AND Logical And 

ASL Arithmetic Shift Left 

ASR Arithmetic Shift Right 

BCC Branch if Carry Clear 

BCS Branch if Carry Set 

BEQ Branch if Equal to Zero 

BGE Branch if Greater or Equal Zero 

BGT Branch if Greater than Zero 

BHI Branch if Higher 

BIT Bit Test 

BLE Branch if Less or Equal 

BLS Branch if Lower or Same 

BLT Branch if less than Zero 

BMI Branch if Minus 

BNE Branch if Not Equal to Zero 

BPL Branch if Plus 

BRA Branch Always 

BSR Branch to Subroutine 

BVC Branch if Overflow Clear 

BVS Branch if Overflow Set 

CBA Compare Accumulators 

CLC Clear Carry 

CLI Clear Interrupt Mask 

CLR Clear 

CLV Clear Overflow 

CMP Compare 

COM Complement 

CPX Compare Index Register 

DAA Decimal Adjust 

DEC Decrement 

DES Decrement Stack Pointer 

DEX Decrement Index Register 

EOR Exclusive OR 

INC Increment 

INS Increment Stack Pointer 

INX Increment Index Register 

JMP Jump 

JSR Jump to Subroutine 

LDA Load Accumulator 

LDS Load Stack Pointer 

LDX Load Index Register 

lsr Logical Shift Right 

NEG Negate 

NOP No Operation 

0RA Inclusive OR Accumulator 

PSH Push Data 

PUL Pull Data 

R0L Rotate Left 

R0R Rotate Right 

RTI Return from Interrupt 

RTS Return from Subroutine 

SBA Subtract Accumulators 

SBC Subtract with Carry 

SEC Set Carry 

SEI Set Interrupt Mask 

SEV Set Overflow 

STA Store Accumulator 

STS Store Stack Register 

STX Store Index Register 

SUB Subtract 

SWI Software Interrupt 

TAB Transfer Accumulators 

TAP Transfer Accumulators to 

Condition Code Reg. 

TBA Transfer Accumulators 

TPA Transfer Condition Code Reg. 

to Accumulator 

TST Test 

TSX Transfer Stack Pointer to 

Index Register 

TXS Transfer Index Register to 

Stack Pointer 

WAI Wait for Interrupt 



75 



The normally high HALT 
line when brought low halts 
the processor and frees the 
system information bus for 
external control. 

The INDEX line is an 
unused one and is provided 
so the pin on each of the 
male connectors may be cut 
with the corresponding 
female connector pins 
plugged, preventing the 
circuit boards from being 
plugged on incorrrectly. 

The IRQ is the maskable, 
single level interrupt request 
line feeding the processor 
board. If not inhibited by 
software it will when 
momentarily given a TTL 
zero level signal, force the 
processor into a push-down 
stack store routine followed 
by a program jump to a user 
selected address stored in 
the operating system RAM. 

The M. RESET line, 
when momentarily 
grounded manually, 
indirectly resets the registers 
internal to the processor 
and interfaces, and loads the 
ROM stored mini-operating 
system. This line is normally 
grounded by depressing the 
RESET button on the 
system's front panel. 



interrupt line feeding the 
processor board. When 
momentarily given a TTL 
zero level it forces the 
processor into a push-down 
stack store routine, 
followed by a program jump 
to a user selected address 
stored in the o perat ing 
system RAM. The NMI is 
not maskable thus cannot 
be inhibited by the 
programmer through 
software. 

§2 is one °f the two 
complementary system 
clock outputs and is used to 
signal that valid _data is _on 
the data lines DO - D7 
when low. 

(|>1 is the non-overlapping 
clock complement of (j)2- 



and is low for a write to 
memory or interface. 



The NMI is the 
non-maskable, single level 



The RESET line when 
low resets the registers 
internal to the processor 
and interfaces, and loads the 
ROM stored mini-operating 
system. This line is activated 
by one shot on the 
M icroprocessor/System 
board when the system is 
first powered up or when M. 
RESET line is momentarily 
grounded. 

The R/W line establishes 
the direction of data flow 
on the eight data lines, DO 
— D7. It is high for a read 
from memory or interface 



VMA is the valid 
memory address line which 
goes low to confirm that 
valid memory address data 
is being presented on the 16 
address lines, AO - A1 5. 

The UD1 and UD2 are 
user defined lines and have 
not been assigned a 
function. 

The —12 and +12 points 
are lines to which an 
isolated ground -12 @ 200 
mA and +12 @ 200 mA 
power supply should be 
connected. The voltages are 
necessary for generating the 
currents required by 20 mA 
current loop Teletype 
equipment on the serial 
interfaces. 

The 7 - 8 VDC UNREG 
point is the line to which a 
+7 to 8 volt dc @ 10 Amp 
unregulated power supply 
should be attached. This 
voltage is then regulated 
down to +5 V dc by 
independent regulators on 
the various boards within 
the system. 

The five 110b, 150b, 
300b, 600b, 1200b lines 
carry 1758.8, 2400, 4800, 
9600 and 19200 Hz clocks 
required by the serial 
interfaces for 110, 150, 300, 



600 and 1200 baud 
communication. 

Also attached to the 
50-line system information 
bus are the interface decode 
and driver circuits. A 
considerable cost savings is 
made here by providing the 
address decoding and 
information bus buffering for 
all of the interfaces right on 
the mother board instead of 
providing it on each of the 
interface boards individually. 
Since each of the parallel 
interfaces require four 
address locations and the 
serial two, four addresses are 
provided for each of the 
interface positions. They are 
assigned as shown in the 
memory map, Fig. 2. 
Interface position 1 (8004 — 
8007) is reserved for the 
terminal control interface. 
The signals carried on the 
interface information bus are 
almost identical to those on 
the system bus. UD3 and 
UD4 are here again User 
Defined data lines and RS0 
and RS1 are Register select 
lines which are identical to 
address lines A0 and A1 
respectively. Power for the 
address decode and buffer 
circuits on the mother board 
is provided by a separate on 
board regulator with a 
current consumption of 
typically 0.4 Amp. ■ 

(More SWTPC 6800 data is 
coming in BYTE.) 



Once youVe assembled 
and checked out the 
operation of your MP-68 
kit, the result will be a 
product which looks like 
this. Note the complete 
absence of most of the 
usual control panel 
functions you might 
expect. This is achieved by 
using a serial communica- 
tions device such as a 
Teletype or an RS-232C 
compatible terminal as the 
"front panel." 




76 



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First Person Report: 



Assembling an 
Altair 8800 



by 

John Zarrella 

90-9 Wakelee Rd. 

Waterbury CT 06705 



I decided I would have 
to opt for a kit . . . this 
would enable me to get 
on line quickly. 



My adventure with 
microprocessors began rather 
late in the hobby game, at the 
end of 1974. It was about 
this time, or so it seemed to 
me, that micros became the 
topic of conversation in 
anything related to 
computers and automation. 
With the IMP-16, the 8080, 
8008, 4004, etc., it became 
clear that this was what the 
computer market was waiting 
for. However, it was the 
article on the MITS Altair in 
the January 1975 issue of 
Popular Electronics which 
finally did it. Although 
inaccurate and vague, it 



certainly decided me — I was 
definitely going to own a 
micro. The next few months 
saw hurried mailings of 
information requests to any 
company which produced a 
product even remotely 
connected with a 
microprocessor. I 
immediately got out my 
checkbook, and mailed all my 
hard earned dollars to every 
newsletter that was 
published, in my frantic 
search for the "right" 
processor. 

The results were both 
rewarding and disappointing. 
I found that there were some 



Fig. 1. The schematic diagram of power supply circuitry, showing 
additional protection diodes. 



+ 8V v 
(UNREG)> 



rr 



iA7805 



^■pCII 

I 35^F 
"* 16V 



R46 
33ft 
+ I6V 2W 
(UNREG)/* ""*- 



ICTE5 



f 



J[ I J^ (REG) 
I CI2 I SCI _[_SC20 



35/iF 
16V 



I.5KEI5 



R45 
220ft 
-I6V . 2W 
(UNREG)/ vvv — 



J *'^ V 



X 



16V 



Jj* (REG) 



TCIO 
35/iF 
16V 



rh i 



I 



C7 

16V 



ICTE5 



n 



D2 
5.1V 



•C9 
35/iF 



rh 16V rh 16V 



-5V 
"* (REG) 



•C8 
•lj*F 



fantastic processors, but since 
my hardware background is 
not all that hot, I decided 
that I would have to opt for a 
kit with one of the most 
powerful micros I could find. 
I figured that this would 
enable me to get on line 
quickly, learn enough 
hardware to keep up with the 
state-of-the-art, and permit 
me to evaluate new micros as 
they came out, so I could 
build my "dream machine" 
when the right parts became 
available. 

I decided to build the 
Altair 8800. Although the 
instruction set looked rather 
impressive, what convinced 
me was seeing a process 
control system which used 
the 8080; I was truly 
impressed with its capability. 

The Order 

After calling in my order 
to MITS, I waited nearly 
seven weeks for delivery. 
MITS did make it within the 
advertised 60-day delivery 
time. All was not roses for 
those seven weeks, however; 
it seems that either MITS or 
Ban kAmericard got their 
signals crossed and couldn't 
get a credit authorization 
(they both eventually 
declined to accept 
responsibility). You can 
imagine what it was like 
getting a call during dinner, 
explaining that my unit was 



78 



ready to ship, but 
unfortunately . . . Luckily 
they agreed to ship it COD, 
and I quickly ran down to my 
bank to get a certified check. 
Every morning I left my wife 
with the admonition not to 
miss the delivery, and every 
day at lunch I called to 
determine whether or not my 
"computer" had arrived. (Did 
you ever try to ask your 
insurance agent whether you 
needed extra renter's 
insurance — "You keep a 
computer at home??!! What 
for?") 

Assembly 

Within a week of that call, 
I had the Altair in my hot 
little hands. "Are those little 
plastic parts all you get for 
$500.00?", my wife 
exclaimed, peering over my 
shoulder. Undaunted, I 
shooed her out and locked 
myself in the back room all 
weekend soldering PC boards. 
It took three weekends to 
complete the assembly (was it 
my fault I came down with 
pneumonia in the middle?). 

Ah yes, assembly. In 
general, I found that the 
MITS assembly instructions 
were well written. However, 
their additions were 
sometimes in the manuals in 
the wrong place (e.g., page 
68A after 69). In at least one 
case (front panel control 
board) I had already 
tightened the panel in place 
(bolts on numerous switches), 
when I read that the nut on 
the little screw holding the 
voltage regulator to the board 
(accessible only with the 
panel out) had to be removed 
to add a grounding strap. 
Therefore it pays to check 
the manual pages carefully, 
and look two or three pages 
ahead to see if there are any 
little tricks sneaking up on 
you. 

As for the parts, only one 
resistor was missing; however, 
out of all the screws and bolts 
supplied with the kit, I could 
never find the right one to fit. 
Maybe it was my own 
stupidity, but it seemed that 



Of all the assembly, the worst (and easiest to mess up) 
part was correctly connecting the 60 bus wires between 
the display /control board and the chassis motherboard. 



the last bolt of any given size 
was always supposed to be 
used in at least 10 more 
places. I found that it pays to 
have a good assortment of 
screws and bolts (number 6, 
various lengths !4" to %") to 
permit f r u st rationless 
assembly. 

All soldering and 
component placement was 
easily accomplished — 
positions were clearly marked 
on the boards and in the 
manual. This is high praise 
since I hadn't built many kits 
before; and of these, none 
were this large. Of all the 
assembly, the worst (and 
easiest to mess up) part was 
correctly connecting the 60 
bus wires between the 
display/control board and the 
chassis motherboard. I used 
an Ohmmeter to assure that 
each connection was correct 
and that there were no solder 
bridges to the other bus lines. 
There's got to be a better 
way. I hear Processor 
Technology, Inc., is currently 
marketing a 16-slot 
motherboard (on the Altair 
you have to jumper four of 
the four slot boards together, 
only one of which comes 
with the kit), and an 
improved connector for the 
display/control board. These 
will definitely be my first 
additions. 

I made only one 
modification to the circuit 
during assembly. That 
modification was to add three 
protection zeners to the CPU 
board. Fig. 1 shows the 
electrical connections for this 
change. These were inserted 
to protect the 8080 chip (still 
pretty expensive in singles) 
from power supply failure. 
These zeners should ground 
out overvoltagcs at currents 
up to 100 Amps. ICTE5s 



were used for the +5 V and 
-5 V lines to the 8080 and a 
1.5KE15 for the +12 V. The 
zeners on the CPU board arc 
illustrated in Fig. 2. 

I also added sockets for 
the 8101 RAMs, cleaned all 
boards with trichloroethylene 
solvent, and inspected the 
finished boards with a 
magnifying glass. I would 
highly recommend these 
procedures as they helped me 
find more than one solder 
splash and cold solder joint. 

The Big Test 

On the fourth weekend I 
got up the courage to mount 
the 8080 and 8101s. Then 
came turning on the power 
and checking voltages. 
Everything looked good, with 
very little ripple from the 



Fig. 2. Detail of the additional protective diodes 

mounted on the Altair CPU board. 



Did you ever try to ask 
your insurance agent 
whether you need extra 
renter's insurance for a 
computer? 



Additional zener 
diodes for overvoltage 

protection. 8080 Central Processor 




79 



Fig. 3. Adding a parallel capacitance of .0047 uF to C8 of the Altair CPU board schematic lengthens the data 
out enable line time so that memory write does not extend longer than the data out time. 



EXM NXT 



DEP 



DEP NXT 






EXM NXT SS 
1/2 71123 
K 



TO 

MWRITE 

LINE 



•5V 



N JD- 





DEP SS 
1/2 74123 



DEP NXT SS 



5 



Rll 



C9 



on-card voltage regulators. 
Finally the big test: Run a 
program. This is where the 
only problem finally showed 
up. I stopped and reset the 
CPU, set the switches for my 
spectacular program (J MP 0) 
and would you believe it, 
"deposit" wouldn't work. An 
hour later I had determined 
that all other panel switches 
worked correctly (including 
deposit next), and that the 
deposit switch itself was in 
good order. In order to 
initially get around the 
problem I had to examine 
location 177777 (all address 
bits 1), then use deposit next 
to get to location 0. 

A study of the schematics 
showed that deposit and 
deposit next use the same 
circuitry, except that deposit 
next first does an examine 
next. You can verify this 
visually by loading all ones 
into the first 10 locations of 
memory. Then, if you use 
deposit next to change all the 
locations to zero, by carefully 
watching the data LEDs, you 
will notice that they all flash 
on as the switch is activated 
(examine next) and 
immediately go off again as 
the deposit is performed. 

I concluded that the 
problem had to be in the 
liming, since the circuits were 



■GND 



C7 R9 





I/2 74I23 

F 



I) 



l-»-W\r 

cio RI2 



■GND 



TO DATA 
OUT ENABLE 
' (SWITCHES 
SA0-SA7) 



I/2 74123 
G 



C8 

.01 /iF 



'►Al-o-vw 



■ GND 



► 5V 



RIO 



-)M MODIFICATION 
C = .0047/iF 



otherwise identical. Sure 
enough, when I looked at the 
signals on a scope, lo and 
behold, when a deposit was 
performed, the memory write 
line was enabled for 
approximately 20 ns more 
than the data out line. There 
are two oneshots in the 
deposit circuit; the first 
enables the memory write 
line, and the second enables 



the data out line. The 
memory write problem was 
cured by increasing the 
capacitance on the second 
deposit oneshot. An increase 
of .0047 uF (which increases 
the data out enable time by 
at least 30 ns) proved 
sufficient. This was obtained 
by adding the .0047 uF 
capacitor as shown in Fig. 3. 
When building the Altair, this 



means that C8 (front panel 
control board) should be 
approximately .0147 uF; if 
the b o a r d is already 
assembled into the case, a 
.0047 uF capacitor can easily 
be soldered onto the back of 
the board without removing 
any components from the 
case. (Be sure to unplug the 
computer before making the 
change, however.) Fig. 4 
shows placement of the new 
capacitor and the change to 
the Altair schematic diagram. 

I feel that the kit is 
reasonably well made and a 
good buy — at least at the 
current 8080 single lot prices, 
though the add-on options 
may cost somewhat more 
than elsewhere. 

My plans for my unit 
currently involve addition of 
vectored interrupts (a 9318 
or 74148 8-bit to 3-bit 
priority decoder is about all 
that's needed to translate the 
eight vectored interrupt lines 
on the bus into an RST 
instruction), a real-time 
clock, monitor clock and 
some type of I/O (teletype, 
CRT, etc.). ■ 



Fig. 4. The additional .0047 uF capacitor is mounted on the rear of the control panel board. 




£ •■ i'~ 



i 



Solder the 
additional capacitor 

to the rear of the 
control panel board. 



Modify this section 
of your schematic. 



80 




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Power Supply: Output: 5-15V @ 600ma. Ripple and 
Noise: less than 20mv @ full load. Load/Line 
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3 



R/C BRIDGE 



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detector, to zero-in on exact component selection . . . 
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DM-3 includes an extensive instruction/applications 
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SPECIFICATIONS 

Resistance Range: 10(1-100 megH. (6 Ranges: 

10-ioon, ioo-iooon, iK-ioKn, iook-1 megn, 1 

megn-10 megO) Capacitance Range: 10pFd-1<mFd- 
(5 Ranges: 10-100 pFd, 100-1000pFd, .001-.01 
mFd, .01m*Fd-.1mFd, .1- 1.mFd.) Null Detector: 2 
hi-intensity LEDs-hi/lo markings. Accuracy: <5% of 
null dial, range switch setting. Wght. 2 lbs. 
Power Needed: 1 17V, AC Sj> 60Hz 3W.* 



Each measures 6.75"L x 7.5"W x 3.25" H.; completely assembled, ready to start 
testing at once. Order your DESIGN MATES today! 
"220V @ 50Hz available at slightly higher cost. 

All DESIGN MATES are made in USA; available off-the-shelf from your 
local distributor. Direct purchases from CSC can be charged on Bank 
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corrrinerrmi /peciniTie; coRPORRTion 

44 Kendall Street, Box 1942, New Haven, CT 06509 • 203/624-3103 
West Coast Office: Box 7809, San Francisco, CA94119 • 415/421-8872 

Canada: Len Finkler Ltd., Ontario 

© Copyright Continental Specialties Corporation 1975 



Can YOUR 
Computer 

Tell Time? 



by 

James Hogenson 

Box 295 

Halstad MN 56548 



FROM MAIN 
PROGRAM 



SET VALUE 

OF 
REGISTER 



DECREMENT 
REGISTER 




Fig. J. The idea of a timing loop, 
or how to make a CPU waste time 
productively. 



RETURN 
TO MAIN 
PROGRAM 



Loops are the basic 
time delay elements. 
Then there are loops 
within loops, loops 
within loops within 
loops and so on ad 
infinitum. 



Can your computer tell 
time? O.K. Now take away 
the LSI clock chip, pocket 
watch, grandfather clock, or 
whatever else you managed to 
interface together. Can your 
computer still tell time? You 
bet it can! 

It is a readily accepted fact 
that almost any type of 
hardware logic device can be 
imitated or simulated by 
computer software. That can 
also include timing devices if 
you wish. 

We will examine a few 
methods and considerations 
for software timing, then 
apply what we've learned in 
making a novel "software 
only" clock which will keep 
time as well as any 
conventional clock. 

The most efficient method 
(efficient referring to 
memory space used) to 



produce a time delay is the 
use of a loop. This loop is 
basically very simple, as 
shown by Fig. 1. By including 
NOPs or other non-functional 
time wasters in the loop, the 
loop can be significantly 
stretched. 

An 8008 is being used in 
the examples in this article, 
but the principles hold for 
any computer. Only the 
numerical values will change. 

The loop represented by 
Fig. 1 for an 8008 would be a 
simple three instructions (six 
bytes) long. 



LBI ~] 

„ x „ LOAD DEL 



AY 

/*• DCB DECREMENT "X" 
' JFZ 

vT L JUMP BACK 

|_ H UNLESS X = 

The value of "x" loaded 
into the B register will be the 
main factor in varying the 
time delay provided by this 
loop. Calculating the exact 
time period is done by 
tabulation of instruction 
execution times. These 
examples will be based on the 
8008 instruction execution 
times with the clock running 
at exactly 500 kHz. 



To calculate the time for 
this loop, assume the value of 
"x" to be 1 so no part of the 
loop is repeated. Add up the 
number of microseconds 
required by each instruction. 

LBI = 32 US 

DCB = 20 US 

JFZ = 36 US 

88 US 

Now go back to determine 
how many microseconds each 
repetition of the loop will 
produce. The LBI instruction 
is not repeated. Do not count 
any unrepeated instructions 
in this second tabulation. 



DCB 
JFZ 



20 US 

44 US 



Note the different 
execution times for the JFZ 
instruction. For the 8008, the 
execution time of conditional 
instructions depends upon 
the condition. If the 
condition results in a true 
branch, the instruction takes 
the longer of the two 
execution times. The false 
branch is the shorter time. 

The time formula for this 
loop is 

64X + 24 = N 



"x" being the value loaded 
into B and "n" being the 
total execution time in 
microseconds. The unreduced 
formula is 

(X - 1 ) 64 + 88 = N 

Since 64 us are added for 
each repetition, we must 
multiply 64 by one less than 
the value of "x." 

255 is the largest possible 
value of "x" since we are 
limited to an 8-bit word. 
Therefore, the maximum 
time delay that can be 
provided by this loop is 
16344 us. This loop can be 
stretched by placing a NOP 
instruction (op code 300) 
before the DCB, and 
re-routing the jump. 



LBI 


SET VALUE OF 


"X 


"x" 






NOP 


ABSORB EXTRA 


20 US 


DCB 


DECREMENT "x 


1 


JFZ 


JUMP BACK TO 


NOP 


L 


UNLESS X = O 




H 







If desired, more than one 
NOP may be inserted. Each 
NOP will add another 20x 
microsedonds. The maximum 
time with one NOP is 21444 
us, the NOP adding 5100 us. 

If a timing loop is to be 
used a number of times at 



82 




various points in a program, it 
may be desirable to rewrite 
the loop as a called 
subroutine. The basic 
flowchart remains unchanged; 
only the method of 
implementing it changes. 

(MAIN 
PROGRAM ) 
CAL CALL 
L TIME 
H LOOP 



SET VALUE OF "x" 

DECREMENT "x" 

RETURN IF "X" = 

JUMP BACK TO DCB 



Tabulation will show that 
the basic loop is good for 1 16 
us with each repetition 
adding 76 us. The reduced 
formula is 

76X + 40 = N 

This loop is a little more 
complex. Although the CAL 
instruction which calls the 
loop is not a part of the loop 
itself, the execution time of 
the CAL instruction is a part 
of the time period produced. 
We, therefore, must add 44 us 
for the CAL. 

As done before, we assume 
the value of "x" to be 1 for 
the first tabulation. The RTZ 
will be a true branch, so we 
stop adding there. An RTZ 
true branch will take 20 us, 
while an RTZ false branch 
will take 12 us. 

Each repetition will add 
12 us for the RTZ, 44 us for 
the J MP, and 20 us for the 
DCB instruction. The 
unreduced formula is 

(X - 1)76 + 116 = N 

NOPs placed before the 
DCB instruction will have the 
same effect as in the first 
loop, an additional 20x us per 
NOP. 

The maximum time period 
produced by this second loop 
with one NOP is 24520 us. 
The minimum time period 
without any NOPs is 116 us. 
Anything under 116 us can 
be more efficiently 
implemented with straight 
NOPs than with a loop, 
should such a need arise. 



If a time period much 
longer than 24000 us is 
needed, modify the time loop 
to make a double loop as 
shown in Fig. 2. Make an 
identical loop, but rather 
than using a NOP for more 
time, insert an entire loop. 



(BEGIN ^ 
LOOP J 



SET VALUE 
OF Y 



SET VALUE OF 



SET VALUE OF 




DECREMENT X 

JUMP BACK TO 
IF "x" * 
DECREMENT "Y 
RETURN IF "Y 

JUMP TO LBI 



DCB 



" = 



Time calculations for 
multiple loops become 
somewhat more complex, but 
again the same principle is 
used. 

The inside loop used here 
is the same loop first 
calculated at the beginning of 
this article. When calculating 
the main loop, the inside loop 
is treated as one combined 
unit of value. The tabulation 
will look like this: 



MAIN LOOP: 
CAL 
LCI 

INSIDE 
LOOP = 
DCC 
RTZ 



44 US 
32 US 

{ 64X + 24 ) US 

20 US 

20 US 
(64X + 140) US 



EACH REPETITION OR 
TRUE BRANCH WILL ADD: 

RTZ = 12 US 

JMP = 44 US 

INSIDE 

LOOP = ( 64X + 24 ) US 

DCC = 20 US 

( 64X + 100 ) US 

The formula, unreduced, 
would be 

64X + 140 + 
( Y-l ) ( 64X + 100) = N 

Reducing the formula 
gives us 

64XY + 100X + 40 = N 




( RETURN J 



Fig. 2. Getting fancy. By nesting one timing loop 
within an outer loop, much longer delays can be 
obtained. Two parameters "x" and "y" are re- 
quired to completely specify this loop. In a 16-bit 
machine, of course, the same result (here intended 
for an 8-bit 8008) can be obtained without nested 
loops since the 16-bitter can count much higher. 



The maximum time delay 
provided by this loop would 
be 4187140 us. A NOP 
inserted at location "a" will 
add 20y us. A NOP at "b" 
will add 20xy us. The use of 
both NOPs will boost our 
maximum time to 5492740 
us, or over 5 seconds. 

The purpose of developing 
formulas is to determine the 
values of the registers needed 
to obtain a specified time 
period. For purposes of 
illustrating an example, let us 
assume we want exactly 5000 
us to pass between point A 
and point B of a program. We 



would place a CAL 
instruction between point A 
and point B which would call 
the time loop. The shorter 
loop will be sufficient for this 
application, so the equation 
will now be 

76X + 40 = 5000 

Working the equation will 
give a value of 65.23615 . . . 
for "x." A fractional value 
will not fit in any single 
register of the CPU. To find 
out what to do now, multiply 
65 by 76, add 40, and 
subtract the result from 
5000. We find the difference 



83 



is 20 us. This is very simple to 
take care of. Insert a NOP 
instruction at any point in 
the routine where it will not 
be repeated. Before the LBI 
instruction would do fine. 
Now, with 65 (decimal 
notation) loaded into the B 
register, exactly 5000 us will 
pass between points A and B 
of our main program. 

Finding an exact time 
period using the longer loop 
involves a certain amount of 
trial and error. To find an 
approximate value of "x" 
(using no NOPs) use this 
formula: 

( N-40 -\ 
* -(-W)- l ' 5 

Assign an arbitrary value 
to "y," replace "n" with the 
required time period. 

Now, assume a time period 
of exactly 505904 us is 
needed. (This time period will 
be used later.) There is one 
stipulation in this case which 
will be explained in greater 
detail later. The value of "x" 
must be 255. Solving the 
formula equation for "y" 

( 64 ) ( 255 )Y + 
100Y + 40 = 505904 

gives "y" a value of 30.8078. 
30 must be used for "y." The 
total time of the loop is then 
492640 us, 13264 us short of 
the required time. In most 
cases, you would re-assign 



values and try again, but in 
this case, the value of "x" 
cannot be changed. The 
alternative is to use the 
shorter loop to clean up the 
leftovers. After calling one 
loop, call the other loop. 
Then go on with the main 
program. Solving the short 
loop equation comes out at a 
nice even 174. 

76X + 40 = 13264 

What looked like a real 
oddball turned out to be 
perfect! 

The formulas and all such 
may seem like a lot of 
monkey business just to 
waste time. Speed is the 
purpose of computers, but 
there are times when they 
must be slowed down. 

The primary application of 
time loops is in I/O interface. 
If a computer is to monitor a 
data input which is to be read 
once every 10 ms, there are 
two alternatives for timing. 
The hardware of the device 
being monitored may include 
a timing device and a flag to 
indicate when the device is 
ready. The computer enters a 
loop which monitors the flag 
until the device is ready, then 
reads the data. The other 
alternative is to use the 
software time loop, and omit 
the extra hardware. 



An interesting application 
along this line is a completely 
software "fabricated" 
keyboard debounce system. 
This method will not work in 
an interrupt type of input 
system, but for many small 
scale systems, this method is 
ideal. 

Rather than connecting 
the key pressed line of the 
keyboard to some debounce, 
timer and latch circuitry, 
connect it to the eighth bit of 
the parallel data input on the 
computer. The loop used will 
test the eighth bit for the 
keypressed state. When a 
keypressed is sensed, a time 
loop of 1 6344 us is executed, 
then the data input is 
accepted. The loop then 
branches back to the main 
program to take care of the 
new data. When the program 
comes back to the input loop, 
the keypressed line is first 
tested to be sure no keys are 
being pressed. After all keys 
have been released, the loop 
will wait for the next 
keypressed state. This 
procedure will prevent more 
than one data entry from 
each keystroke. 

When I first tried this 
keyboard debounce method 
over five months ago, I was so 
pleased with it that I'm still 



Fig. 3. Software can be used to debounce a keyboard — simply loop 
around for a long enough time to ensure that keys have stabilized. The 
loop is started as soon as the "any key pressed" (keypressed) line 
indicates any non-null bit pattern. 




TEST INPUT FOR KEYPRESSED. 
WAIT UNTIL CONDITION IS 
SATI SFIED 



TEST INPUT FOR KEYPRESSED, 
WAIT UNTIL CONDITION IS 
SATI SFIED 



EXECUTE 

TIME 

DELAY 



ACCEPT INPUT OF DATA 

JUMP TO MAIN PROGRAM 
(MAY BE REPLACED WITH A 
RETURN INSTRUCTION.) 



INCREMENT 
TIME 
COUNT 






I 






UPDATE 
DISPLAY 




' 




INITIATE 
TIME 
CYCLE 







Fig. 4. The digital clock program 
looks simple at this level: Incre- 
ment the time count, update the 
display, then initiate a time cycle 
such that the entire loop takes 
exactly one second! 



using the method for all data 
entry to my microcomputer. 
Not once has it missed some 
data, or given me false or 
duplicated data. And it was 
so easy to implement! 

Time loops may also be 
used in output applications. I 
have an SWTPC TV 
typewriter, but I am not 
using the special computer 
interface board. I found that 
a simple time loop does the 
job well enough and fast 
enough. 

Since we've done our 
homework, now we can play. 
An interesting and novel 
application of time loops is a 
completely software 
"fabricated" clock. The clock 
program presented here will 
have three major functions 
(see Fig. 4). 

The clock will display 
hours, minutes and seconds. 
The "increment time count" 
segment of the program is 
responsible for computing the 
next time reading in 
sequence. It must consist of 
more than a straight counting 
sequence since time is not 
expressed in straight decimal 
format. 

The "update display" 
segment is responsible for 
producing the newly 
computed time at an output 
device. 

After the first two 
segments have been executed, 



84 



Fig. 5. Ah, but the simplicity of Fig. 4 - as this figure reveals - hides a tot of low level detail. Here is the flow chart of the clock's operations. 



E> 



r 



1-1-3 

5 3 

< 





oia: 

<3 — 
WOO 



Wo)l_ 

LuncD 



< 
Q. 




Ld ■ 

\- L 

<iu: 







H 




/ 


H 


HI 




s 




ujOq 


or 

o 


IT 


^ 


O 




X 





85 



8008 Timing Quick Reference Guide 

US . INSTRUCTION 

20 INCREMENT INDEX REGISTER 

20 DECREMENT INDEX REGISTER 

20 ROTATE ACCUMULATOR 

12/20 CONDITIONAL RETURN* 

36/44 CONDITIONAL JUMP* 

36/44 CONDITIONAL CALL* 

20 UNCONDITIONAL RETURN 

44 UNCONDITIONAL JUMP 

44 UNCONDITIONAL CALL 

20 RESTART 

32 LOAD DATA IMMEDIATE 

(INTO INDEX REGISTER) 

36 LOAD DATA IMMEDIATE 

(INTO MEMORY REGISTER) 

32 ALU IMMEDIATE 

20 ALU REGISTER 

32 ALU MEMORY REGISTER 

24 OUTPUT 

32 INPUT 

20 LOAD DATA - REGISTER(OP CODE 3--) 

32 LOAD DATA - MEM. E REG. (OP CODE 3-7 OR 37-) 

Here is a quick reference table for execution times of all instructions 
in the 8008 repertoire. Such a reference table can be easily made for 
any CPU. Simply multiply the number of machine states required 
for the execution of each type of instruction by the time required 
per machine state. AT 500 kHz, the 8008 takes four us per machine 
state. An unconditional jump instruction requires 11 states in the 
8008 , therefore 44 us. Do not confuse machine states with machine 
cycles. The same jump instruction requires three machine cycles. 

'Conditional instructions: Execution time depends upon condition. 
If condition causes true branch, the execution time is longer. If the 
condition causes a false branch (if condition is not satisfied), the 
execution time is shorter. 



the "time cycle" segment 
makes up the difference so 
that the entire program takes 
exactly one second per pass. 
Writing a clock program isn't 
hard, but making it take 
exactly one second per pass 
definitely adds to the 
challenge. The major 
consideration is that branches 
from conditional instructions 
must be balanced in such a 
way that the program will 
take exactly the same 
execution time regardless of 
the combination of 
conditions and branches. 
That's where all the time 
loops come in, and that's 
where lots of fun comes in! 
The program can best be 
described in the form of a 
flowchart, Fig. 5. The 
program listing in Fig. 6 is 
divided according to the 
flowchart divisions shown by 
dashed lines. The op codes 
are for 8008 systems. The 
mnemonics and op codes can 
be easily translated into 8080 
format. However, all timing 
considerations must be 
recalculated for use with 
anything other than an 8008 
running at exactly 500 kHz. 



When time balancing a 
segment of a program, it is 
best to work from the 
bottom and go up. The time 
adjustment in part A of the 
flowchart must compensate 
for parts B, C, D and E, so 
before that time period can 
be calculated, the execution 
time of the other parts must 
be calculated. 

Some of the time 
adjustments in part E do not 
use a time loop. The short 
time adjustments there (in 
part E) are more conveniently 
implemented with a 
combination of other time 
consuming instructions which 
will not change the function 
of the program. 

To determine the time 
adjustment needed in one 
branch, tabulate the total 
execution time of the longer 
branch. Add or subtract 8 us 
(depending upon which 
branch is the true branch) to 
compensate for the difference 
in conditional j ump 
instructions. 

The same time loop will be 
used several times, yet the 
time periods will vary. This 



can be accommodated when 
using the short loop by 
placing the LBI instruction 
and loading the value of "x" 
before the loop is called. The 
location of the LBI 
instruction will have no effect 
on the overall time period 
produced. 

Occasionally a time loop 
will not come out evenly. For 
example, another 12 us may 
be needed. This will not be 
accommodated in the loop, 
so the only alternative is to 
use a NOP instruction. But 
the only instruction which 
will absorb just 12 us is an 
unsatisfied conditional return 
instruction. Using such an 
instruction could result in 
trouble if used alone. 
However, if an AND 
instruction can be used 
without affecting the 
program functions, the AND 
instruction will insure that 
the conditional return (RTC) 
will not be satisfied. To keep 
the program in balance when 
balancing the time, insert a 
NOP in the opposite branch 
to offset the AND 
instruction, and the net 
difference will be 12 us. 

Flowchart parts F and G 
need not be included in the 
time balancing considerations 
of A, B, C, D and E. The 
program returns to a common 
point before executing parts 
F and G, so those parts are 
not offsetting anything. 

The output loop as given 
in the listing will provide an 
ASCII output for a TV 
typewriter. A sufficient time 
loop is provided between 
each individual output 
operation. The output loop 
may be easily modified for 
use with other devices. For 
use with Teletype, a linefeed 
command must be added to 
the output characters. (Only 
a carriage return is used with 
a TVT.) For use with an LED 
display, deleting the ORI 
instruction at location 
04/257 will leave a straight 
binary (also BCD equivalent, 
since vales do not exceed 9) 
output. Keep in mind, 



however, that modifying any 
part of the program will also 
require modifying the timing 
elements involved. 

The execution time of the 
complete "increment time 
count" segment plus the 
"update display" segment 
totals 494096 us. Subtract 
that time from one second to 
find the time required of the 
timing cycle. The required 
time is 505904 us. The values 
for this loop have already 
been worked out in a 
previous example. 

The reason the value of 
"x" cannot be conveniently 
changed in the long loop in 
this case is that the loop is 
called and used from two 
locations in the program. The 



value of 



cannot be 



changed for one application 
without affecting the other. 
If the loop were modified to 
load B from another register 
which remained constant, 
both values would become 
variables which could be 
easily assigned values from 
any point in the program. 
This would also include 
recalculating the time 
formula of the loop. 

Your clock should now be 
ready to run. (Oh, by the 
way, there is one little 
drawback: Your computer 
can't be used for anything 
else while it's keeping time, 
unless, of course, you really 
want to go to extremes with 
the calculating! This program 
is strictly a novelty!) When 
you are ready to start your 
clock, load the correct time 
plus a couple of minutes into 
memory locations 04/000 
through 04/005. When the 
loaded time comes, start the 
computer. Jump into the 
program at 04/006. 

The time kept by the 
computer will only be as 
accurate as the frequency of 
the clock driving the CPU. 
The oscillator must be set at 
exactly 500 kHz. Although 
this is difficult to do, any 
percentage of error in fre- 
quency will be directly 
reflected by the time kept. ■ 



86 



Fig. 6. And finally, the lowest level of detail of all: A "pseudo 
assembly" listing of the program for the digital clock as implemented 
for an 8008 computer. Of course, those readers who have an 8080, a 
650 J, a 6500 or PACE will have to do a little bit of thinking to adapt 
Fig. 4 and Fig. 5 to the alternative microcomputer CPU designs. 



1 HOUR :00t/ OQO 
HOUR : 00*-/ 001 
TM]N: 001/002 
MINiOO4/0O3 
TSEC ; 004/004 
SEC :001/005 

START : 001/006 

©004/007 
004/0] 
004/01 1 
001/012 i 
001/013 : 
004/014 

004/015 : 

001/016 : 

004/017 : 

004/020 : 

004/021 i 

004/022 s 

004/023 = 

004/021 : 

004/025 = 

004/026 * 

004/027 = 

004/030 = 

001/031 = 

004/032 a 

04/033 = 

004/03 4 = 

004/035 = 

GTENS : 004/036 = 

004/037 = 

004/010 = 

001/041 ; 

004/042 = 

004/043 = 

004/044 = 

©004/045 = 

004/046 = 

004/047 = 

004/050 = 

004/051 = 

004/052 = 

004/053 = 

004/054 = 

004/055 = 

004/056 = 

004/057 = 

004/060 = 

004/061 = 

004/062 = 

GQMINi 004/063 = 

004/064 = 

004/065 = 

004/066 = 

004/067 = 
004/070 



XXX 
XXX 
XXX 



056 
004 
066 
005 
307 
004 
001 
074 
01 2 
1 00 
036 
004 
370 
370 
016 



300 
300 
1 04 
275 
004 
006 
000 
370 
061 
307 



© 



004 
004 
004 
004 

004 



004 
004 



GTENMj 00' 



004 
004 



004 



/071 
/072 

073 
074 
075 
/076 
/077 
/ 100 
/ 101 
/102 
'103 
/I 04 
/105 
/ 1 06 
/107 
/l 1 
/111 
/I 12 
/l 1 3 

/l 14 

/I 15 

/I 16 

/I 1 7 



071 
006 
1 00 
063 

004 

370 
01 6 
01 5 
1 06 
247 
004 
1 04 
275 
004 
076 
000 
061 
307 
004 
001 

074 
012 
1 00 
1 1 
004 
370 
01 6 

1 2 

1 06 
247 
004 
3 1 7 
1 04 
275 
004 
300 
006 
000 
370 
061 
307 
004 
001 



©004/ 120 
004/121 
004/ 122 
004/ 123 
004/ 124 
004/ |25 
004/ 126 
004/ 127 
004/ 1 30 
004/ 1 31 
004/ ] 32 
004/ i 33 
004/ 134 
004/ 135 
004/ 136 
GDHOURi 004/ 137 



© 



004/ 1*0 
00*/ 1*1 
004/ 1*2 
00*/ 1*3 
00*/ 1** 
00*/ 1*5 
00 */ 1*6 
00*/l*7 
00*/ 150 
00*/ 151 
00*/ 152 



006 
1 00 
1 37 
004 
370 
016 
007 
1 06 
247 



275 
004 
006 
000 
370 
061 
307 
00* 
001 
370 
06 1 
307 
07* 
001 



H( 5EC ) 

LL I 

L I SEC ) 



10 HOUR DIGIT REGISTER 
HOUR DIGIT REGISTER 
1 MINUTE REGI STER 
MINUTE REGISTER 
10 SECOND REGISTER 
SECOND REGISTER 

LOAD L/H WITH 
ADDRESS OF SECONDS 
DIGIT REGI STER 



INCREP 
DIGIT 



ENT SECONDS 



£— 



DECISION: JUMP IF 
SECONDS DIGIT IS NOT 
LESS THAN 10 



RETURN SECONDS DIGIT TO ITS REGISTER 
REPEAT INSTRUCTION FOR MORE TIME 



CALL TIME LOQP TO COMPENSATE 
'LOOP 
NEED A LITTLE MORE TIME 

FINISHED THIS CYCLE 



CLEAR SECONDS DIGIT REGISTER 



INCREMENT 

10 SECONDS DIGIT 



004/ 1 53 

004/ 1 5* 

004/ | 55 

004/i5 6 

004/ 157 

004/, 60 

004/1 61 

004/162 

004/ J 63 

004/ 1 64 

004/165 

004/J66 

004/167 ; 

4/170 : 

4/171 : 

004/172 i 

004/173 i 

4/174 ! 

004/1 75 - 

004/176 ' 

: 004/1 77 : 

004/200 = 

004/201 = 

004/202 = 

004/203 = 

004/204 - 

004/205 = 

004/206 = 

004/207 = 

004/210 = 

004/21 1 = 

004/2 1 2 = 

i 004/2 i 3 = 

004/211 = 

004/215 = 

004/216 - 

004/217 = 

004/220 = 

004/22 l = 

004/222 a 

004/223 = 

004/224 = 

004/225 = 

004/226 s 



060 
307 
071 
01 2 
1 00 
1 77 



307 
307 
307 
307 
300 
300 
1 04 
275 
004 
006 
000 
370 



^NO 



004 



227 



CP1 DECISION: JUMP IF 

"6" 10 SECONDS DIGIT IS NOT 

JFC LESS THAN 6 



RESHOUR 



004/230 
004/231 
004/232 
004/233 



004 



234 



:}- 



LMA 
LBI 



GOMIN 

RETURN 



10 SEC. DIGIT TO REGISTER 



LMI 
"0" 
DCL 



CPI 

" 1 0" 

JFC 



LBI 
" 1 0" 
CAL 



SET VALUE OF X 
CALL TIME LOOP 

TLOOP 

FINISHED THIS CYCLE 

DISPL 

CLEAR 10 SEC. DIGIT REGISTER 
(LAI, LMA ARE USED INSTEAD OF LMI 
WHERE TIMING WORKS OUT'BET-ER THAT WA 
INCREMENT 
MINUTES DIGI T 

DECISION: JUMP IF 
MINUTES DIGIT IS NOT 

LESS THAN 10 

GTENM 

RETURN MINUTES DIGIT TO REGISTER 

SET VALUE OF "x" 
CALL TIME LOOP 



004/235 
004/236 
004/237 
004/240 
004/24 I 
004/242 
004/243 
004/24 4 
004/245 
4 / 2 4_6 

TLOOPs 004/247 
004/250 
004/251 
004/2S2 
004/253 



DUTL 



h}— 



NEED AN EXTRA 12 US. 

(LBM - 32 US P OTHER 20 US 

I SPL 



BALANCED BY NOP ! 



20 US BALANCE 



NOP 

LAI 

"0" CLEAR MINUTES REGISTER 

LMA 

DCL 

LAM INCREMENT 

ADI 10 MINUTES DIGIT 

" 1 " 



CPI 

"6" 
JFC 



LMA 
LBI 



NOP 

JMP 



DECISION: JUMP IF 

10 MINUTES DIGIT IS NOT 

LESS THAN 6 

GOHOUR 

RETURN 10 MIN. DIGIT TO REGISTER 

SET VALUE OF "x" 

CALL TIME LOOP 



© 



© 



KEEPING THE TIME IN BALANCE 
FINISHED THIS CYCLE 



004/256 
004/257 
004/260 
004/261 
004/262 
004/263 
004/264 
004/265 
004/266 
004/267 
004/270 
004/271 
004/272 
004/273 
004 /2 7_4_ 
004/275 
4/276 
004/277 
004/300 
004/301 
004/302 
004/303 
004/ 304 
004/ 305 
004/ 306 
004/ 307 
004/ 3 1 
004/31 I 
004/312 
004/ 31 3 
004/ 314 
004/ 315 
004/ 316 
004/ 31 7 
004/320 
004/321 
004/322 
004/323 



LMA 
DCL 
LAM 
ADI 
" 1 " 
LMA 
DCL 
LAM 
CPI 
" l" 



DISPL 

CLEAR 10 MINUTES REGISTER 



INCREMENT 
HOURS DIGIT 



PUT THE HOURS DIGIT BACK FOR THE 
TIME BEING. 



LTIMEi 
LTIM1 : 



00< 



/ 324 



004/325 
004/326 
004/327 
004/330 
004/331 
004/332 
004/333 
004/ 334 
004/335 
004/336 
004/END 



060 
307 
074 
003 
1 00 
232 
004 
01 6 
002 
1 06 
24 7 
004 
1 04 
275 
004 
006 
001 
370 
061 
006 
000 
370 
24 1 
043 
04 3 
1 04 
275 
004 
1 1 
053 



307 

064 
060 
121 
026 
005 
1 06 
324 
004 
031 
053 
060 
1 04 
256 
004 
036 
006 
066 
000 
1 06 
256 
004 
006 
01 5 
121 
026 
036 
1 06 



01 6 
255 

1 06 



006 
004 
016 
377 
01 1 

1 1 
326 
004 

02 I 
053 



DEC l c irN; JUMP J F 

HOUR DIGIT is NOT 



L]— -GTENH 



LAM 
LAM 
LAM 
LAM 
NOP 
NOP 
JMP 



WASTE 
200 US 
TO 



BALANCE 
BRANCH 
NOW LET'S GET OUT 
DI SPL 



A NOP IS ADDED TO BOTH BRANCHES 
TO BALANCE THE TRUE BRANCH FROM 
04/153. A BETTER PLACE FOR The' NOP 
WOULD HAVE BEEN 04/156, BUT whD 
WANTS TO REWRITE ha L F a PROGRAM TO 
SAVE ONE MEMORY LOCATION? 



HERE 



001 

370 
300 



DCL 
LAM 
ADI 



NOP 
JMP 



f;J— OISPL 



CLEAR HOUR DIGIT REGISTER 



INCREMENT 

1 HOUR DIGIT 



RETURN 10 HR. DIGIT TO REGISTER 
CYCLE FINISHED 



CPI DECISION: JUMP IF 
"3" HOUR DIGIT IS NOT 
JFC LESS THAN 3 



SET VALUE OF X 
LL TIME LOOP 



"~ TL0 
JMP 



JUMP TO 004/275/036 
"DISPL 
LAI 



1 

LMA 
DCL 



LMA 

NDB 



RESET HOUR DIGIT TO 



CLEAR 10 HOUR DIGIT REGISTER 



RTC 
RTC 

JMP 



DI SPL 



(YES, 241 = 241; THAT'S NOT AN ERROR! 
FOR TIME BALANCING. THE NET DIFFERENCE 
BETWEEN BRANCHES FROM 04/153 WAS 24 US. 
2 X RTC = 24 US. THE NDB IS BALANCED 
BY THE NOP'S MENTIONED 
IN THE NDTE * * * 
DCB SHORT TIMING LOOP 
RTZ 
JMP 

-OOP 



LAM OUTPUT SUBROUTINE STARTS 
ORI GENERATE ASCII CHARACTER 



DCD 
RTZ 



PRINT CHARACTER 

SET VALUE OF "r" 
CALL LONG TIME LOOP 
LT I ME 

ARE WE DDNE PRINTING? 
CONTINUE IF NOT 



DUTL 

LDI SET UP COUNT - DISPLAY ROUTINE 

"6" 

LLI SET UP ADORESS 

"o" 

CAL OUTPUT ROUTINE 



L ""OUT 
hJ 



" 1 3" 

OUT 

LCI 



LB I 
" 1 75" 
CAL 



LBI 
"255" 

DCB 



DCC 
RTZ 
JMP 



H 



OUTPUT CARRIAGE RETURN COMMAND 



SET VALUE OF "y" 
CALL LONG TIME LOOP 



SET VALUE OF "X 
CALL SHORT TIME LODP 

TLOOP 

JUMP BACK TO THE BEGINNING AND RECYCLE 

TART 

SET VALUE OF "x" 

DECREMENT "x" 

JUMP BACK TO DECREMENT AGAIN 

LTIM1 

IF "x" DOESN'T EQUAL "o" 

DECREMENT "y" 

GO BACK TO PROGRAM IF Y = 

REPEAT LOOP 
LTIME 



DECISION! JUMP IF 
10 HOUR DIGIT = 1 



T THE TIME A MINUTE OR TWO IN ADVANCE AT LOCATIONS 04/005, 
IT UNTIL THE RIGHT TIME, AND START THE PROGRAM BY JUMPING 
AT 04/006. THE PROGRAM IS STOPPED BY LOADING A HALT 
STRUCTION INTERRUPT FROM THE FRONT PANEL. 



87 




Getting Started in TTL 

Digital logic is one of the 
many fascinating aspects of 
electronics. To date, TTL 
logic is the heart of almost 
every home brew computer 
system. Programming a 
computer is an exciting 
exploration into a mysterious 
world. Exploring the world of 
hardware that makes the 
programming possible is quite 
another exciting adventure. 
The best way to explore 
either of these worlds is not 
just through reading 
manufacturers data, but 
through experimenting for 
yourself. 

A TTL integrated circuit is 
a simple device by itself. 
When combined with a 
number of devices, a very 
complex system can evolve. 
Don't let the complexity of a 
computer system get you 
down. You don't need to be 
able to design computer 
systems to start having fun 
with TTL. Nor do you need 
be an electronic engineer. 
You don't need to know how 
to build automobile engines 
to get your car started, do 
you? 

To get started, you need 
only a few items. You will 
need a +5 volt power supply 
rated at 1 Amp or so. TTL 
integrated circuits do not 
require anything near 1 Amp 
each, but a number of lCs 
used together may add up to 
more than 1 Amp. 

The most convenient 
method for mounting and 
connecting integrated circuits 
is the use of a solderless 
terminal strip, the type 
advertised in BYTE and many 
other electronics 
publications. Only a little 
wire (22 or 24 gauge wire) is 
needed for interconnecting 
the TTL devices. 




A good starting selection 
of TTL integrated circuits 
might include the following. 



Exploring the world of 

hardware with a dc power 

supply and a solderless 
terminal strip. 



quantity 


type 


2 


7400 


2 


7404 


2 


7408 


2 


7410 


2 


7411 


1 


7420 


1 


7421 


1 


7473 



description 

Quad 2-input pos. NAND gate 
Hex inverter 

Quad 2-input pos. AND gate 
Triple 3-input pos. NAND gate 
Triple 3-input pos. AND gate 
Dual 4-input pos. NAND gate 
Dual 4-input pos. AND gate 
Dual J-K flip flop 



The 7400 series part 
numbers are standard. 
Different manufacturers may 
add one or two letters to the 
number, but it is still the 
same part. 

A TTL device has only 
three types of connections: 
Input, output and power 
supply terminals. The power 
supply terminals will be 
ground (GND) and Vcc. The 
voltage applied to Vcc should 
be +5 for proper operation. 

The inputs and outputs 
will always be in one of two 
states: HIGH or LOW. In the 
HIGH state, the voltage will 
be over 2.4 volts. In the LOW 
state, the voltage will be 
under 0.4 volts. Only a simple 
LED is needed for a state 
indicator. The circuit design 
physics are simple: Connect 
the output of one device 
directly to the input of 
another device, provided the 
TTL ICs used are not the 
open collector type. The ICs 



listed above are not the open 
collector type. 

Your next most important 
item will be your literature. 
There are many details not 
discussed here which you will 
want to learn as you advance 
in TTL designing. There have 
been many books written on 
the subject of TTL. One very 
good book for hobbyists is 
Don Lancaster's TTL 
Cookbook, which provides 
much information valuable to 
newcomers to the field, yet is 
detailed enough to be of great 
value even after you are quite 
familiar with TTL. 

A second source of 
information is a TTL data 
book, available from the 
manufacturers. Most TTL 
suppliers will supply data 
sheets for free or for a 
nominal fee. A data book is a 
complete collection of data 
sheets for all TT L 
manufactured by the 
company you obtained the 
book from. The data sheets 



or book will show the logic 
diagram, actual circuit 
diagram, pin connections, and 
circuit characteristics and 
functions for each TTL 
device. 

Your own experience 
should be proof that TTL is 
no more difficult than any 
other aspect of computers. So 
start planning your 
expedition! 



REFERENCE BOOKS 
ON TTL 

Texas Instruments Inc. 
PO Box 3640 M/S 84 
Dallas TX 75285 

TI supplies the following ex- 
cellent references. To order send a 
personal check or money order to 
the above address. 

LCC4200 Semiconductor 
Memory Data Book, $2.95. 

LCC4151 Linear & Interface 
Circuits Data Book, $3.95. 

LCC4111 TTL Data Book, 
$3.95. 

LCC4161 Supplement to the 
TTL Data Book, $1.95. 

TTL Cookbook, by Don Lan- 
caster. Howard IV. Sams & Co., 
Indianapolis, Indiana, 1974. 
$8.95. See the review in BYTE 
#1, page 85, for details about this 
excellent introductory text and 
reference source. 

Use of ASCII Approved for 
Amateur Satellites 

The FCC has issued a 
Special Temporary Authority 
(STA) to the Radio Amateur 
Satellite Corporation 
(AMSAT) allowing the use of 
ASCII by radio amateurs 
through the communications 
packages aboard the OSCAR 
6 and OSCAR 7 satellites. 
The STA has been granted 
until Feb. 28, 1976. At the 
conclusion of this period, 
AMSAT will compile a report 
of the results of the 
experiments conducted and 
callsigns of the amateurs 
involved. More information 
can be obtained from 
AMSAT, Box 27, Washington 
DC 20044 phone (202) 
488-8649. 

Gary L. Tater W3HUC 
7925 Nottingham Way 
Ellicott City MD 21 043 



88 







Micro-440 

Computers come in all 
sizes. Here is a product made 
by COMP-SULTANTS Inc., 
PO Box 1016, Huntsville AL 
35807. The product is the 
Micro-440 computer, based 
upon the Intel 4040 chip, and 
is to my knowledge the first 
such kit available. The photo 
shows an assembled version 
of the product, which costs 
$375 including 256 bytes of 
RAM program memory, 
power supply, cabinetry and 
displays. The entire CPU is 
constructed on one PC board. 
A kit version is available at 



$275, and COMP-SULTANTS 
will sell partial kits as well. 

Information can be had 
for 25?! in coin, or you can 
order the user's manual 
(440-U) for $10, which is 
refundable with an order for 
the product. 

The Intel 4040 instruction 
set operates upon 4-bit words 
in scratch pad register areas, 
and will prove adequate for 
many of the simpler program- 
ming applications readers 
might contemplate. It will 
prove to be an excellent 
learning machine at a fairly 
reasonable price. 



Try to Duplicate This Using 
Magnetic Tape! 

William D. Roch (5133 
Catalon Ave., Woodland Hills 
CA 91364) sends in this 
sample of an ASCII character 
set translated into codes 
which will punch real dot 
matrix letters on paper tape. 
It provides a way for people 
with paper tape equipment to 
put a human-readable leader 
onto a tape prior to punching 
the usual data. 

In order to conveniently 
use this method, you'll have 
to make a table in memory to 
contain the full 6-bit ASCII 
subset shown in the table. 
Then you'll have to write a 
little routine to take a 
character string input 
parameter, look up each 
character in the table, and 
output the appropriate 
sequence of codes. The table 



A 


= 


5)>I I>S 


SPACE 


= 


a a a a a a 


B 


= 


a?%s:Za 




! 




aWa 


C 


= 


a~! !Ra 




" 




aGaGa 


D 


= 


a? ! !^a 




H 


= 


aJ?J?Ja 


b 


= 


a?%s ! a 




s 


= 


aRj;?)Pa 


F 


= 


a?EEAa 




% 


= 


aSK42a 


G 


= 


a^! ) : Ha 




& 


= 


a^-^ [ s 


H 


= 


a?DD?a 




t 


= 


aGa 


1 


= 


a ! ? ! a 




( 


= 


a "> ! a 


J 


= 


aP ?a 




) 


= 


a ! "a 


K 


= 


a?LR!a 




* 


= 


aRL?LRa 


L 


= 


a? a 




= 


- 


aLLLa 


M 


= 


a?BDB?a 




- 


= 


aDODa 


N 


= 


a?BDH?a 




a 


= 


a\" - . Pa 


U 


= 


a? ! ! ?a 




1 


= 


a? ! a 


P 


= 


a?I IFa 




\ 


= 


aADH a 





= 


a A ! i>a 




+ 


= 


ai . sa 


R 


= 


a?IY&a 






= 


a rt >a 


S 


= 


aV+ )Za 




/\ 


= 


asB?Bsa 


1' 


= 


aAA?AAa 




1 


= 


a ! ?3 


U 


= 


a? ?a 




< 


= 


aLR ! a 


V 


= 


aOP POa 




> 


= 


a!RLa 


w 


= 


a?PHP?a 






= 


axes 


X 


= 


a ! RLR ! a 






= 


aXXa 


Y 


= 


aAB<BAa 




? 


= 


aBA )Fa 


I 




ai ) %u a 

l = 


a ! ? 

S9%? 


/ 

"a 




a HDAa 






3 = 


a ! xxis 










4 - 


aHL. 


?Ha 








5 = 


aWK- 


Ya 










6 = 


a-^Kxxa 










7 = 


aAAoGa 










8 = 


aZ%% 


Za 










9 = 


aF ) ) 


« a 







lists what looks like gibberish, 
but when you punch out the 
sequences shown, you will see 
character patterns in the 
holes on the tape. 



Creative Uses of DIP Header 
Plugs 

Sumner S. Loom is 
(Loomis Laboratories, Box 
131-A, Prairie Point MS 
39353) sends along three 
different examples of DIP 
header plugs used to mount 
components in existing 
circuitry. The first, A, is a 
plug-in substitute for an 
operational amplifier — a 
simple resistor used in an 
existing circuit which did not 
need the op amp. B is an 
example of how a socket can 
be attached to a DIP header 
plug in order to partially 
rewire a circuit without 
touching the original wiring. 



B 



Several of the socket pins are 
bent and connected directly 
to the same pins of the plug. 
Other socket pins are clipped 
and rewired to different pins 
of the plug. By saving the 
original wiring, this technique 
leaves you the option of 
going back to the original IC 
— or you can use this 
technique to correct for 
errors in a PC board. The 
example of C shows several 
resistors mounted on the 
plug. This technique of 
mounting small discretes on 
plugs enables you to use 
sockets for these parts. It 
saves the hassle of installing 
individual wrapping posts. 



Notes 



As BYTE #4 goes to press, 
Electronic News (Sept. 29, 
1975) is running an 
advertisement for the 
Advance Micro Devices 
version of an 8080 design: 
The Am9080A. Significant is 
that the 1 00 quantity price of 
this chip is now down to 
$29.95. Price drops go even 
further than that — if you 
want to buy a million of the 
processors, you'll get a real 
bargain at $6 each. 

This is further evidence 
that the cost of silicon in a 
home computer is getting 
closer and closer to the cost 
of the iron used to contain it. 

* * * 

"... But the roots of the 
software misery go deeper. It 
comes from the fact that 
people are forced to live with 
machines that they do not 
want. They have not 
constructed them, they 
simply receive them and have 
to make the best out of it . . . 
Thus, software engineering, 
for the time being, is partly a 



defense stratagem. But, I 
hope that some day this 
situation will turn around, I 
hope one day software 
engineering considerations 
will dictate how machines are 
to be built and then to be 
used . . ." 

Friedrich L. Bauer in the 

Preface to 

Software Engineering, An 

Advanced Course, 

Springer-Verlag Publishers, 

1973. 

* * * 

"A lot of comparisons have 
been made about how much 
faster computers can do 
things than humans can. Here 
is another aspect of this 
comparison: To make all the 
errors a modern computer 
can make in 10 seconds, it 
would take a team of 30 
accountants working full-time 
for 50 years." 

Barry W. Boehm, Guest 

Editor, 

IEEE Transactions on 

Software Engineering, 

Vol. SE-1, No. 2 (June 

1975), p. 137. 




Welcome, 

IBM, to 

personal 

computing 



With the announcement of 
the IBM 5100 system in a 
press release dated Sept. 9, 
1975, personal computing 
gains an entry from the 
industry's production and 
service giant, IBM. The IBM 
5100 is being marketed 
primarily as a problem solver 
for industrial, commercial 
and professional people — 
with the result that it is a 
very professional package at a 
premium price. But you will 
get a lot of function when 
you buy one of these 
computers — and you'll be 
able to call upon IBM's 
longstanding reputation for 
good service and customer 
handholding, the points 
which have led to the 
commendable success of IBM 
as a computer company. 

What IBM engineers have 
done is to design a 50 
lb-package of interactive 
personal computing which 
includes the following major 
features as standard items: 

• System software is 
built-in, with access to 
BASIC and/or APL 
depending upon options 
purchased. These languages 
and the necessary monitor 
programs arc hardwired into 
a read only memory. 

• A video screen is built-in, 
with up to 1024 characters 
displayed in a 16-line by 
64-charactcr format. 




• An interactive keyboard is 
standard, including the 
usual text entry section as 
well as a separate calculator 
style keypad. The keyboard 
has special function coding 
for all the APL and BASIC 
syntax elements. 

• User memory starts at 
16K bytes in the minimum 
configuration and can be 
expanded to 64K bytes 
(65,536). 

• A magnetic tape cartridge 
storage device is standard. 
This is built into the unit, 
and becomes the primary 
method of storing user data 
and programs. It is also used 
to load IBM supplied 
programming packages. The 
cartridges for this device 
hold up to 204,000 
characters of information. 



You get all this function 
and professionalism from 
IBM by paying a high price. 
This machine is not intended 
to be a toy, although it would 
make an excellent one. It is 
intended as a production tool 
for people who presently use 
lime sharing terminals, 
programmable calculators or 
other personal computers in 
daily work. Prices mentioned 
in the press release are: 

• IBM 5100 processor . . . 
$8975 to $19,97 5, 
depending upon user 
memory (16K, 32K, 48K or 
64K bytes) and language 
(APL or BASIC or both) 
options. 

• IBM 5103 printer ... 
$3,675 purchases an 80 cps 
132-column dot matrix line 
printer. 




• IBM 5106 Auxiliary tape 
unit . . . $2,300 purchases 
an additional tape cartridge 
drive to augment the 
functions of the built-in 
drive. 

• "Problem Solver Library" 
software is available For a 
one time rental of $500 
including a wide range of 
utility and applications 
software with interactive 
user sequences. 

Miscellaneous features also 
available for the machine 
include a TV monitor output, 
the external I/O adaptor used 
with the 5103 and 5106 
devices, a communications 
adaptor which makes the 
5100 emulate an IBM 2741 
communications terminal, 
and a carrying case. 

As an IBM engineered 
product, you can expect a 
solidly built computer. If you 
are a business or professional 
person needing a high quality 
calculational and 
programming tool, then you 
should investigate the 5100 as 
an item of capital equipment 
— which you can incidentally 
use to program numerous 
BASIC games when you're 
not using it for business. But 
if your sole interest in the 
machine is as a luxury toy, 
you have to be moderately 
well off to purchase the IBM 
5100 al its present price. ■ 



90 



THERE'S SOMEONE WHO WORKS FOR 
YOU WHO HAS CANCER. AND 
DOESN'T KNOW IT. HELP FIND HIM. 



You don't know who he is. He 
doesn't know who he is. But 
there is a way to find him. 

By letting us help strengthen 
your employee health program 
with our Employee Education 
Program. The purpose of the 
program is simple. We want to 
save lives by exposing your 
employees to sound facts and 
recommendations for action 
about cancer. 

We'll supply free films, ex- 
hibits, speakers, pamphlets, 
posters, articles for your com- 
pany publications. 

We'll help you arrange 
"action" programs for your em- 
ployees... clinics to help ciga- 
rette smokers quit, instruction 
in breast self-examination, 
screenings for cervical cancer 
via the Pap test. All with one 
purpose: to educate your peo- 
ple about the lifesaving facts 
of cancer. 

Because if cancer is detected 
in its early stages, chances for 
cure are markedly increased. 

For more information contact 
your local American Cancer 
Society Unit. 

You will have helped to save 
someone's life. 

Maybe, even your own. 



i 

AMERICAN 
CANCER SOCIETY 




91 




111 j*g» 




Hit the deck in shorts and 
a tee shirt. Or your bikini if 
you want. 

You're on a leisurely cruise 
to remote islands. With names 
like Martinique, Grenada, 
Guadeloupe. Those are the 
ones you've heard of. 

A big, beautiful sailing vessel 
glides from one breathtaking 
Caribbean jewel to another. 
And you're aboard, having 
the time of your life with an 
intimate group of lively, fun- 
loving people. Singles and 
couples, too. There's good food, 
"grog',' and a few pleasant 
comforts. . .but there's little 
resemblance to a stay at a 
fancy hotel, and you'll be 
happy about that. 

Spend ten days exploring 
paradise and getting to know 
congenial people. There's no 
other vacation like it. 
Your share from $245. A new cruise is forming now. 
Write Cap'n Mike for your free adventure 
booklet in full color. 



H 




Windjammer Cruises. 



A WINDJAMMER INTERNATIONAL SUBSIDIARY • OTC 



City 



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Zip 



Phone 



P.O. Box 120, Dept. 121 



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92 



Shipmates 



to join'baref oot'expediiion 




And, we'll promise you only one thing. The most adventurous vacation you have 
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A congenial group of shipmates now forming and setting their heading for Saba, 
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Explore pink, white and black sand beaches. Scale the cliffs, climb a volcano, prowl 
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Send me your color brochure on 10 day 'barefoot' vacations from S250. 



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Post Office Box 120, Depi. 00, Miami Beach, Florida 33139. 



93 




Fig. 1. One of the most convenient but permanent methods of assembly for experimental 
computer systems and logic designs is wire wrap construction using sockets and a general purpose 
prototyping board. This photograph illustrates an overall view of a partially wired Motorola 6800 
computer system fabricated on a board available from CELDAT Design Associates, Box 752, 
Amherst, N.H. This board provides a basic socket mounting matrix for 14 and 1 6 pin sockets plus 
a general purpose area in the center which will accept bigger sockets. 

The board which was photographed for this photo essay is the prototype Motorola 6800 system 
which is being designed and constructed for the LIFE Line application. 



Photographic Notes on Prototype Construction 



by 

Carl Helmers 

Editor, BYTE 




Fig. 2. As photographer Ed Crabtree zooms in for a closer 
look, we see details of several useful techniques. These 
techniques can be used with any one of several brands of 
general purpose boards which are available from manufac- 
turers. 

Sockets can be mounted by carefully soldering the four corner 
pins of the pads in the socket patterns of the general purpose 
# board. 



In the typical general purpose board, power and ground 
distribution is provided by alternate printed circuit strips on 
the wiring side of the board. Short jumper wires are wrapped 
to the socket pin and soldered to the appropriate bus as shown 
by the examples in the foreground. 

Before wiring, a sheet of paper can be punched with a socket 
pattern using a spare socket and some perforated board. After 
cutting the paper to size and writing an identifying number for 
the circuit, the resulting label is slipped over the pins. 

Several examples of two-level wire wrap interconnections can 
be seen in this photograph. The typical wire wrap post can 
accommodate three levels but good practice limits the use to 
two levels as a general rule. 



94 




SHARE 
BYTE 



The next time a friend wants to borrow your BYTE sit right down and buy him a 
subscription and gel him oft' your back. You know darned well that he isn't going to give 
you back your magazine, so be practical about it. 

Subscriptions are only $ 1 2 cheap enough to spread joy and fun among a few friends 

like for Christinas. Tell you what the second and onward subscriptions will only be 
$10 - Christmas Special good until the end of the year. 

A subscription makes a great Christmas present because the recipient gets a reminder 
every month for a year of your thoughtfulness. 

Be a saint. 



r 



j~GIFT 

I Name . . 

I 

| Address . 

I City . . . 



"1 



Cut 



Tear 



Name . . 
Address . 
City . . . 



State . 



.Zip. 



. State . 



Zip. 



□ BILL ME DCheck for $12 enclosed 

□ Bill BankAmericard or MasterCharge #. 



[□BILL ME □ Check for $10 enclosed 



I J 



GIFT Shred 

Name 

Address 

City State . 

□ BILL ME □ Check for $10 enclosed 



Zip. 



| GIFT 
Name . . 

| Address . 
City . . . 



Rip 



. State . 



I 

| n BILL ME □ Check for $10 enclosed 



Zip. 



_J. 



95 



• BYTE • Peterborough NH 03458 



'fi* F ' 




Fig. 3. It is good construction practice with logic circuitry to heavily bypass the 
logic power supplies. This is especially true of TTL logic, but applies as well to any 
of the alternative logic families. This photo shows how a typical "decoupling 
capacitor" of .1 uF is connected between a power bus and the ground plane of the 
board. The power bus runs between the rows of integrated circuits. 




Fig. 4. A technique which is 
often useful in wiring a neat 
board is the use of wiring 
guides. This photo illustrates 
one very inexpensive way to 
make such a guide - bend a 
short piece of wire such as a 
clipped resistor lead to shape 
then solder it to the 
prototyping board's ground 
plane. In this picture the 
wiring guide is shown before 
any wires have been added in 
its vicinity. 




Fig. 5. As wiring progresses, 
the wiring guides placed at 
strategic places on the board 
come into use and become 
filled with bundles of 
interconnection wire as in 
this photograph. After the 
system is completely 
debugged, the two ends of 
the guide can be bent down 
over the bundle. Until then 
they are left open at the top 
so that new wires can be 
slipped in. 



96 



THE 

CURVE TRACER 

THAT WON! 

COLLECT DUST. 




The Hickok Model 440 
semiconductor curve tracer is 
all purpose and convenient to 
use. It's the ideal instrument for 
testing, evaluating, classifying 
and matching all types of 
transistors, FET's and diodes. 
You'll get stable, full range 
dynamic displays that you can 
accurately scale right from 
the screen. 

■ Pull-out card for easy, fast 
set-up and operation. 

■ Set-up marks for rapid set-up 
of 80% of tests. 

■ Unique INSTA-BETA display 
takes the guesswork out of 
transistor and FET parameter 
measurement. 

■ In-or-out of circuit testing. 

■ A full range professional 
tracer at a price you can 

afford ' $1fW>0 

AT YOUR DISTRIBUTOR *J.U*J 

HICKOK 

the value innovator 

INSTRUMENTATION & CONTROLS DIVISION 
THE HICKOK ELECTRICAL INSTRUMENT CO. 
10514 Dupont Avenue • Cleveland, Ohio 44108 
(216)541-8060 • TWX: 810-421-8286 



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TO MATCH 8800 

• TWO 4k BLOCKS OF DYNAMIC R.A.M. 

• USER OR FACTORY ADDRESS PROGRAMMING 
(SPECIFY) 

• EACH CMR-8080-8k is SHIPPED WITH AN EDGE- 
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• EXPANDER BOARDS AVAILABLE (ADDS FOUR 
SLOTS TO 8800) 

TEN REASONS TO CHOOSE 
THE CMR MEMORY CARD 

1. 300ns ACCESS TIME 

2. TWICE THE MEMORY DENSITY 

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4. DESIGNED FOR THE 8800 

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10. 90 DAY WARRANTY ON PARTS AND LABOR 



"ORDERING NOTE: 

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97 




What You Can Do With an Oscilloscope Graphics Display 

Sumner Loomis, Route 1, Box 131, Prairie Point MS 
39353, supplies us with some additional illustrations of what 
can be done with the oscilloscope graphics display unit he 
built based upon the design of Jim Hogenson in BYTE #2. The 
barking poodle is self-explanatory. The second picture is a 
histogram of some experimental data which is being displayed 
by the graphics output device. 




16K MS MOM KIT 
LESS THAN 5.5 C! WORD 

16,384 8-BIT WORDS ON 
ON ONE CARD WITH PIGGY-BACK ONLY 

$895.00 

• PLUG DIRECTLY INTO 8800 

• LOW POWER: + 8 TO +10V, LESS THAN 600 mA 

+15TO+18V, LESS THAN 100 mA 
-15 TO-18V, LESS THAN 30 mA 

• TOP 4K WITH PROTECT-UNPROTECT 

• USES LOW POWER SCHOTTKY TTL 

• MEMORY CHIPS SOCKET MOUNTED 

• 50/50 GOLD-PLATED EDGE CONTACTS 

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• JUMPER PROGRAM 16K ADDRESS SLOT 

• 8080 HOME BREW COMPATIBLE 

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INTRODUCTORY SPECIAL ON ORDERS 
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Course in Virginia 

A course entitled "Digital 
Electronics for Automation 
and Instrumentation" will be 
given at Virginia Polytechnic 
Institute and State 
University, Blacksburg VA, 
on Dec. 7-12, 1975. 
Instructors are David G. 
Larsen, Dr. Peter R. Rony, 
Jonathan A. Titus and Dr. 
Frank A. Settle Jr. The 
course uses Bugbooks I, II 
and /// as text (see review of 
Bugbook III on page 108). 
The course is an "in-depth 
laboratory/lecture course 
[which] provides hands-on 
experience with the wiring of 
digital circuits of modest 
complexity involving popular 
and inexpensive TTL 
integrated circuit chips . . ." 
Enrollment is limited to 24 
persons, $325 to members of 
the American Chemical 
Society, $360 to 
non-members. To register or 
obtain additional 
information, contact Harold 



Walsh at the Education Dept., 
American Chemical Society, 
1155 16th St., N.W., 
Washington DC 20036 
(phone 1-202-872-4600). 
Technical questions about the 
course can be answered by 
calling Mr. Larsen at 
1-703-951-6478 or Dr. Rony 
at 1-703-951-6756. 

Out of Context . . . 

A. M. Biguity provides 

BYTE with the following 

note which he found in the 

Fairchild Semiconductor 

34000 Isoplanar CMOS Data 

Book, page 2-8: 

"Individuals and tools 

should be grounded before 

coming in contact with 

34000 devices . . ." 

"The trend is to stay upwards 
compatible with all previous 
bugs." 

Prof. Niklaus Wirth in a 
1972 compiler 
construction course at 
Stanford University. 



98 



JAMES ELECTRONICS 

P.O. BOX 822 BELMONT. CALIFORNIA 94002 

(415) 592 8097 



WALL or T.V. DIGITAL CLOCK 

12 or 24 Hour, 25' VIEWING DISTANCE, Walnut Case-6"x3"xV 
Hr. & Min.-6" High, Seconds-3" High 
Kit-All Comp. & Case - $34.95 
Wired & Assembled - S39.95 



POCKET CALCULATOR KIT 

5 function plus constant-addressable memory with 
individual recall— 8 digit display plus overflow- 
battery saver-uses standard or rechargeable batteries- 
all necessary parts in ready to assembly form- 
instructions included. 3"x SV»" 
SPECIAL S12.95 each 

OPTIONS- 115 VAC Transformer 4.95 each 

6 each "N" Alkaline Batteries .... 1.95 lot 



^ 



11 Hies a MAN3 rudotlt to 

if the following states by then 

1 (LOW)-o (PULSE)-P The 
tact high frequency ' ,ulses '° 
an'l be used .1! MOS levels at 



LOGIC PROBE 



,^> 



printed circuit board $9.95 Per Kit 



MINI POWER SUPPLIES 

These power supplies offer small size, with a wide choice ot voltage outputs. 
They ate all capable of delivering 300mA ami have dimensions ol 1" x 1" x 3". 
The voltages available are +5V, -5V, +6V, -6V, -H2V, -12V. All ol ihess units 
easily assemble in less than a half an hour, because of the fiberglass printer! 
circuit hoard construction. Picnic specify voltage when ordering. 



$9.95 per kit 



LOW COST DIGITAL CLOCK KIT 

Other companies have altered a low cost digiial clock kit. but da no: alter 
mportam extras such as, primed circuit boards, power supplies cases, etc. We 
at James arc doing just Ihe opposite by offering a complete clock kit, that 
includes everything down to the line cord. This kil uses .25" END 70 displays, 
for HOURS, MINUTES, and SECONDS, in conjunction with the MM53H clock 
chip. The printed circuit board is of high quality fiberglass, which is plated. The 
case is a 6 x IV; x 1 walnut case with a plexiglass Iron t, and is similar to the one 
in Dur TV WALL Digital clock. K is available wilbnut the case for S1B.95. 



$19.95 per kit. 



ELECTRONIC ROULETTE 

Complete kit 
with all 
components 
case and 
transformer. 




8" x 8" x 1" 
A 56 page book on the facts 
of Roulette included. $29.95 Per Kit 



ELECTRONIC CRAPS 



& m 




Complete kit 
with all 
components 
case and 
transformer. 



oe- 



A 56 page book on the facts ' 

of Craps included. $19.95 Per Kit 



Satisfaction Guaranteed. $5.00 Min. Order. U.S. Funds. 
Add $1.25 for Postage — Write for FREE 1976 Catalog 
California Residents — Add 6% Sales Tax 

P.O. BOX 822, BELMONT, CA. 94002 
PHONE ORDERS - (415) 592-8097 



DIGITAL 

PERFORMANCE 
YOU CAN RELY ON 




The Hickok Model 334 DMM is 
a rugged, non-temperamental, 
hardworking tool that's easy to 
use and easy on your eyes. 
Hickok has established a unique 
reputation in digital electronics 
during the past 10 years. The 
Model 334 is another example 
of our engineering expertise — 
an economical lab quality 
instrument with exceptional 
durability and accuracy. 

■ Easy reading, green 
fluorescent display 

■ 3 1 /2 digit — auto polarity 

■ 26 ranges including 200 mV 
AC & DC ranges 

■ Fast response — 
2.5 readings/sec 



Basic Accuracies (% of reading) 


DC Volts; ±0.2% (±0.5% on 200V, 


1200V ranges) 


AC Volts; ±0.5% (±2.0% on 


200 mV, 2V ranges) 


OHMS; ±0.5% 


DC Current; ±1.5% 


AC Current; ±2.0% 



AT YOUR DISTRIBUTOR 



$22900 



HICKOK 



the value innovator 

INSTRUMENTATION & CONTROLS DIVISION 
THE HICKOK ELECTRICAL INSTRUMENT CO. 
10514 Dupont Avenue • Cleveland, Ohio 44108 
(216) 541-8060 • TWX: 810-421-8286 



99 




Clubs and Newsletters 



San Diego Club Activities 

The San Diego Computing 
Society (for lack of a more 
permanent name) sent BYTE 
a copy of an August 1975 
newsletter. The newsletter 
included information on club 
activities as well as a lengthy 
and wide-ranging comparison 
of various alternatives for 
microprocessor users, written 
by member Dr. Michael 
Hayes. The article covered 
possible choices from existing 
uP evaluation kits to the 
LSI-11. News of club 
activities in eluded a 
scheduled meeting with 
speakers from Processor 
Technology Inc. to 
demonstrate their products 
which included the new 
TV-Dazzler color television 
graphics display device. For 
information on the San Diego 
Computing Society, write: 

Gary Mitchell 

Box 35 

Chula Vista CA 9201 2 
Membership dues (which 
bring the newsletter to your 
mailbox) are $2.50. 



Southern Florida Club? 

Roberto R. Denis (1 1080 
N.W. 39 St., Coral Springs FL 
33065) inquires about club 
activity in southern Florida. 
He's interested in contacting 
persons and starting a club. 

Denver Amateur Computer 
Society 

George Mensik, proprietor 
of Gateway Electronics in 
Denver, called BYTE as #4 
goes to press. He reports a 
large and active Denver Ama- 
teur Computer Society exists 
(over 100 members) with 
interest in computer 
activities. The DACS 
meetings include talks by 
industry people as well as 
tutorial sessions and special 
interest gatherings. George's 
store also serves as a general 
meeting ground for the 
Denver area. 

You can find out about 
the DACS by contacting 
George at Gateway Elec- 
tronics, 2839 W. 44th Ave., 
Denver CO 80211 (phone 
1-303-458-5444). 



News from the Southern 
California Computer Society 
The September 1975 issue 
of Interface, the SCCS's lively 
newsletter, arrived as BYTE 
#4 was being assembled in 
late September. The SCCS 
people have put together an 
excellent and informative 
club letter — running 15 
pages in the Vol. 1 No. 1 
issue, just for September. In 
addition to reports on club 
business matters, the major 
portion of the letter concerns 
information and background 
data of general interest. The 
newsletter is sent to 
members. To become a 
member, send $10 annual 
dues plus your complete 
name, address, zip and 
telephone information to: 

Southern California 

Computer Society 

PO Box 987 

South Pasadena CA 91030 

In phone conversation with 
Hal Lashlee of SCCS 
(I -21 3-682-31 08) BYTE 
learned a few details of the 
group purchase of Digital 
Equipment Corporation 
LSI-1 I computer equipment. 
The basic deal is that the 
SCCS will pool individual 
orders for the DEC 
equipment to obtain quantity 
discounts at the 50-, 100- and 
possibly 200-level price 
breaks. Orders will be made 
initially on the assumption of 
50-quantity purchases, at the 
following prices for 
equipment: 

LSI-11 CPU (4K x 16 
memory, PDP-11/40 
instruction set), $653. 
LA-36 DECWriter (30 CPS 
terminal), $1480. 

The SCCS is in the process of 
securing a fidelity bond for 
the offer, and, according to 
Hal, has made arrangements 
for MasterCharge and 
BankAmericard payment for 
orders. A fee for the service — 
intended as a contribution to 
the club's activities — is set at 
a minimum 2% of the order 
value. Larger contributions 




are of course solicited to help 
pay for the club's operation. 

It also looks as if the SCCS 
will be starting the first active 
LSI-11 computer users group 
as a result of this purchase 
activity. 

If you're interested, Hal 
says that inquiries 
accompanied by a large self 
addressed stamped envelope 
should be sent to the 
Southern California 
Computer Society at the 
address above. 

New England Computer Club 
An organizational meeting 
of the New England 
Computer Club has been 
scheduled for Nov. 5, 1975. 
A tentative meeting place, 
arranged by Ted Poulos of 
Brookline MA, is at the 
Jarrell-Ashe plant, Waltham 
MA. Boston and southern 
New Hampshire area 
computer hackers who want 
to be on the mailing list for 
future meetings should send 
their name and address 
information on an index card 
or IBM card to: 

New England Computer Club 
c/o BYTE Magazine 
Peterborough NH 03458 

Chicago uP Users Group 

The Chicago Area 
Microcomputer Users Group 
met for the first time in 
September, with about 30 
attending. For latest 
information, contact Bill 
Precht, 1102 S. Edson, 
Lombard I L 60148. 



100 



MC 14412 UNIVERSAL MODEM CHIP 

MC14412 contains a complete FSK modu- 
lator and de-modulator compatible with 
foreign and USA communications. (0 — 600 
BPS) 
FEATURES: 

• On chip crystal oscillator 

• Echo suppressor disable tone generator 

• Originate and answer modes 

• Simplex, half-duplex, and full duplex 
operation 

• On chip Sine Wave 

• Modem self test mode 

• Selectable data rates: - 200 

0-300 
0-600 

• Single supply 

VDD = 4.75 to 15 V DC -FL suffix 
VDD=4.75to6 V DC -VL suffix 
TYPICAL APPLICATIONS: 

• Stand alone — low speed modems 

• Built-in low speed modems 

• Remote terminals, accoustical couplers 

MC 14412 FL 28.99 

MC 14412 VL 21.74 

6 pages of data 60 

LED Mounting Hardware 
(Specify bezel color) 

1750-04 (4 readout) $ 7.00 

1 750-06 (6 readout) $ 9.00 

1 750-08 (8 readout) $1 1 .00 

Screen available in red, amber or neutral color 

2102-1 MEMORY 
1K fully encoded fast (500ns) MOS RAM. 
New factory prime parts . . .$4.15, 10/$39.00 



MC14411 Bit Rate Generator. Single chip for 
generating selectable frequencies for equip- 
ment in data communications such as TTY, 
printers, CRT's or microprocessors. Generates 
14 different standard bit rates which are 
multiplied under external control to 1X, 8X, 
16X or 64X initial value. Built-in crystal 
oscillator circuit. Operates from single +5V 
supply. 
MC14411P with specs $22.40 



Output Ratal (Hz) 


X64 


X16 


X8 


X1 


614.4 k 


153.6 k 


76.8 k 


9600 


460.B k 


115.2k 


57.6 k 


7200 


307.2 k 


76.8 k 


38.4 k 


4800 


230.4 k 


57.6 k 


28.8 k 


3600 


153.6 k 


38.4 k 


19.2 k 


2400 


115.2 k 


28.8 k 


14.4 k 


1800 


76.8 k 


19.2 k 


9600 


1200 


38.4 k 


9600 


4800 


600 


19.2 k 


4800 


2400 


300 


12.8 k 


3200 


1600 


200 


9600 


2400 


1200 


150 


8613.2 


2153.3 


1076.6 


134.5 


70355 


1758.8 


879.4 


109.9 


4800 


1200 


600 


75 


921.6 k 


921.6 k 


921.6 k 


921.6k 


1.843M 


1.843M 


1.843M 


1.843M 



Clock Chip. The MM5318 is an excellent 
choice for TOD clock all by itself. The display 
interface has externally selectable character. 
This allows for outputting one digit at a time 
to the BCD or 7 seg busses under external 
control. Useful for computer real time clocks, 
TV display, serial character transmission. With 
specs. 
MM531 8 Clock Chip $7.40 




RECEIVER 
TRANSMITTER 

UART-1013A is an ideal device for driving 
computer peripherals such as teletypes & 
video terminals. NEW, factory fresh parts. 
Made by General Instruments. Full specs. 
New low price! 
URT-1 01 3 A $1 0.95, 2/$1 9.95 




ASCII KEYBOARD ENCODER 

National MM5740AAE. Complete keyboard 

interface system capable of encoding 90 single 

pole single throw switch closures into 9-bit 

ASCII code. Silicon gate technology and is 

TTL input compatible. Has N Key rollover, 

one character data storage, repeate function, 

capacitor key bounce masking, with spec 

sheet. 

MM5740AAEN $19.95 



INTERSIL 8038CC 

Precision Waveform Generator/Voltage Con- 
trolled Oscillator. 

Wide Frequency Range of Operation 0:001 
Hz to 1.5 MHz 

Variable Duty Cycle 1% to 99% 

#IIC8038 . . . with specs $3.95 



7 SEGMENT DECODE/DRIVER/LATCH 



Fairchild 9374 TTL/MSI is a 7 segment 
decoder driver incorporating input latches and 
output circuits to directly drive common 
anode LED displays. Constant current 15 mA 
sink eliminates need for matching resistors. 
Automatic zero blanking. Transparent latches. 
Pin compatible with SN7447. 
FDL-9374 $2.99 

TV CLOCK CHIP SET. Display time of day 
directly on your TV screen. MM5318 and 
MM5841 ICs form the basis for video display 
clock. 5318 keeps time of day (4 or 6 digit) 
and 5841 provides display video signals with 
sync derived directly from your set. Makes 
most interesting way to tell time of day 
during TV hours. 
MM5841/MM5318 Set with specs . . . $20.80 




I C SOCKETS. 
PC Mount . . . Solder 
Skt-0802 ... 8 pin . . 
Skt-1402. . . 14 pin. 
Skt-1602. . . 16 pin . 
Skt-1802. . . 18 pin . 
Skt-2202 ... 22 pin . 
Skt-2402 ... 24 pin . 
Skt-4002 ... 40 pin . 
Wire Wrap Tails 
Skt-1400. . . 14 pin . 
Skt-1600. . . 16 pin . 



HIGHEST QUALITY! 
Tail 
254, 10/$2.25 
. 264, 1 0/$2.40 
. 304, 10/$2.70 
.454, 10/$4.25 
.604, 10/$5.50 
. 654, 10/$6.00 
.$1.25, 10/$11.00 

. 494, 10/$4.50 
. 554, 10/$5.00 



EXAR! 

XR-320 Precision timer $1.55 

XR-2240 Prog. Counter/timer 4.80 

XR-210 FSK Demodulator PLL 5.20 

XR-205 Waveform Generator 8.40 

XR-2206 Function Generator 5.50 

XR-2207VCO 3.85 

EXAR XR-2206KA Function Gen Kit. 
Includes monolithic function generator IC, PC 
board, parts list and assembly instruction 
manual $1 9.95 

PRECISION LAB QUALITY REGULATOR 
MC1466L chip can be used to build a high 
quality voltage and current adjustable power 
supply. Available output current limited only 
by the supply and the number of pass 
transistors. Floating type regulator allows 
voltage variation from to 250V! .01% line 
and load regulation. 
MC1466L w/specs $8.55 

DUAL ± 15V TRACKING REGULATOR 
MC1468L 14 pin DIP Package. 
FEATURES: 

Output current to 100 mA > 

•Line and load reg. .06% 

•External adj 8 to 20V 

•Remote sensing 

MC1 468 L w/specs $4.95 



T0-92 VOLTAGE REGULATORS 

If your project needs only 100 mA or less, use 

these tiny plastic regulators right on your PC 

board. Same size as a plastic transistor. Save 

space and $. Last 2 digits denote voltage 

(positive). 

LM78L05, LM78L12, LM78L15. 854 

1/2A Regulator. Fairchild 78MGT2C positive 
and 79MGT2C negative regulators are adjust- 
able from 5V to 30V with only 2 external 
resistors. Only 1 resistor for +5V (±.2V) from 
the 78 MGT2C. Comes in 8 pin minidip 
package format with heat tabs for attaching 
to PC board or heat sink. Easily connected for 
± tracking supplies. 
78MGT2C (pos) or 79MGT2 (neg) $2 



5V, 3A T0-3 Regulator. Fairchild SH323KC 
monolithic regulator in TO-3 power package. 
Use it with the same ease of installation as the 
famous 309K (same pin arrangement). Take 
care of those heavy current requirements 
without separate regulator/pass transistor 
combinations. 
SH323K3 5V, 3A $9.95 



MINIATURE ROCKER DIP SWITCHES 
Dual in-line SPST switch arrays for P.C. 
mounting. Spring loaded sliding ball contact 
system for positive, tease proof contact. 
Comes in contact arrangements from 4 to 10 
per pack. Fits standard DIP sockets. Last two 
digits of stock Vindicate number of switches. 

DIS-76B04 $3.10 

DIS-76B06 $3.50 

DIS-76B07 $3.75 

DIS-76B08 $3.95 

DIS-76B10 $4.35 




tRi tek, inc. 



P.O. BOX 14206, DEPT 7 PHOENIX, ARIZONA 85063 



101 



•••■■■II 
•lllllll 



the 6000 SERIES 

COMPUTER FAMILY 



■iimii 



OHIO SCIENTIFIC INSTRUMENTS IS NOW OFFERING A COMPLETE 

LINE OF PIN COMPATABLE BUS ORIENTED 8BIT lMhz MICROPROCESSORS 

AND SUPPORT CHIPS BY MOTOROLA, AMI, MOS TECHNOLOGY AND OTHERS. 

EACH MICROPROCESSOR COMES COMPLETE WITH SUPERBOARD: 

A COMPLETE MINICOMPUTER P.C. BOARD (DOUBLE SIDED EPOXY ) 

WHICH ACCEPTS ANY 6000 SERIES PROCESSOR, SYSTEM CLOCK, 

2- 1702 TYPE ROMS, IK X 8 RAM (2102 TYPE), 1 PIA , 1 ACIA, CURRENT 

LOOP AND PARALLEL INTERFACES AND HAS BUS EXPANSION CAPABILITIES. 



6800 

6501 AND SUPERBOARD- DIFFERENT INSTRUCTION 
SET, BUT JUST AS FAST 

6502 



AND SUPERBOARD- •THE TOP OF THE LINE" 99 

49°" 
54 00 



AND SUPERBOARD- A 6501 WITH INTERNAL 
CLOCK 



ALSO AVAILABLE- 
SYSTEM MONITOR ROMS, PROMS, RAM, PIAs, ACIAs, UARTs , 
AND BUS TRANSCEIVERS 
RAM- ROM MEMORY EXPANDER BOARD 

SUPER I/O BOARD CONTAINING CASSETTE INTERFACE; X,Y DISPLAY 
AND A/D CONVERTER . 

COMING SOON- 
VIDEO GRAPHICS BOARD 
FIRMWARE BASIC BOARD (USES ROM AND CALCULATOR CHIP) 

ALL CHIPS ARE FULL SPEC. INDUSTRIAL QUALITY COMPLETE WITH FACTORY 
SPEC. SHEETS, SUPERBOARD, AND OUR OWN APPLICATION SCHEMATICS 
AND NOTES. 

CALL (216)-653-M8<* OR WRITE TODAY FOR OUR FLYER AND OUR NEW 
APPLICATIONS NOTE "THE 6000 SERIES BUS." 



D5I 



OHIO SCIENTIFIC INSTRUMENTS 



P.O. BOX 374, HUDSON. OHIO 44236 




NEVER YOU MINI) 




OCCUPANT 
BOX BYTE 
PETERBOROUGH 
NH 03458 



BIT COLLECTING 

Editor, 

First let me congratulate 
you and your staff on an 
extremely interesting and 
informative first issue. It is 
definitely the best first issue 
of a magazine that I have ever 
read. I, like thousands of 
others, decided on 
subscribing to BYTE after 
collecting a few bits of 
information concerning what 
you intended to publish. I 
was very pleased to see that 
you managed to get all the 
bits together to form a 
BYTE! I believe that while 
the MITS people have set the 
standard for "the affordable 
computer," the BYTE people 
are now setting the standard 
of how to educate people in 
using it! 

1 was particularly 
interested in the comments of 
one reader regarding the 
playing of games between 
computers. I intend to 
develop a CHESS program for 
my Altair 8800, probably in 
MITS 8k BASIC language. I 
would like to correspond 
with all the people out there 
who share the same interest. 
While on this topic, I should 
say that I would like to see 
some competitions between 
small computers classified 
according to core size, 
instruction set, cost or 
whatever else will encourage 
people to pack the most 
efficiency and genius into the 
lowest cost system. 

In closing, I must make 
one final observation. I 
noticed in Don Lancaster's 
article on "Serial Interface," 
p. 35 [BYTE #1], that the 
originate modem tx and 
answer modem rx frequencies 
do not agree as is necessary 



for proper operation. The 
answer modem receive 
frequencies should be 1070 
Hz space and 1270 Hz mark. 
Incidentally, I thought the 
article by Don was of his 
usual high calibre and should 
serve as an example for others 
to follow. 

Dan Clarke 

105 Fir Court 

Fredericton NB 

Canada E3A 2E9 



DOWN ON EARTH? 

Editor, BYTE: 

1 ordered my subscription 
to BYTE when the first ad 
was printed in 73 Magazine 
last summer. The first book I 
got was #2 (October 1975). 
Where is my #1 ? Please send 
it. 

I have a good 
understanding of analog and 
logical circuitry — i.e., gates, 
counters, shift registers, 
radio, TV and machine 
control. But — 

The only down on earth 
articles from which I got the 
full meaning in issue 2 were 
"Television Interface" (best 
by far), "Quick Test of 
Keyboards,'' and 
"Asynchronitis." 

Please — I want to 
understand 8008 and 8080. 
What's inside, relating to the 
logic I know? When are they 
called for? And what must be 
used with them? 

Most articles start in the 
process of program 
development — much too late 
for the beginner. It seems 
many cute words add to the 
snow: Like byte, Basic, life, 
architecture, kluge??, 
algorithm, subroutines, 
language — various, 



102 



I 5% OFF ON ORDERS OVER $50.00 
I 10% OFF ON ORDERS OVER $100.00 
I 15% OFF ON ORDERS OVER $250.00 

n 



TTL 
















7451 


.17 


74154 


1.25 


7400 % 


.14 


7453 


.17 


74155 


1.07 


7401 


.16 


7454 


.17 


74156 


1.07 


7402 


.15 


7460 


.17 


74157 


.99 


7403 


.16 


7464 


.35 


74158 


1.79 


7404 


.19 


7465 


.35 


74160 


1.39 


7405 


.19 


7470 


.30 


74161 


1.25 


7406 


.35 


7472 


.30 


74162 


1.49 


7407 


.35 


7473 


.35 


74163 


1.39 


7408 


.18 


7474 


.35 


74164 


1.59 


7409 


.19 


7475 


.57 


74165 


1.59 


7410 


.16 


7476 


.39 


74166 


1.49 


7411 


.25 


7483 


.79 


74170 


2.30 


7413 


.55 


7485 


1.10 


74173 


1.49 


7416 


.35 


7486 


.40 


74174 


1.62 


7417 


.35 


7489 


2.48 


74175 


1.39 


7420 


.16 


7490 


.59 


74176 


.89 


7422 


.26 


7491 


.97 


74177 


.84 


7423 


.29 


7492 


.71 


74180 


.90 


7425 


.27 


7493 


.60 


74181 


2.98 


7426 


.26 


7494 


.94 


74182 


.79 


7427 


.29 


7495 


.79 


74184 


2.29 


7430 


.20 


7496 


.79 


74185 


2.29 


7432 


.23 


74100 


1.30 


74187 


5.95 


7437 


.35 


74105 


.44 


74190 


1.35 


7438 


.35 


74107 


.40 


74191 


1.35 


7440 


.17 


74121 


.42 


74192 


1.25 


7441 


.98 


74122 


.45 


74193 


1.19 


7442 


.77 


74123 


.85 


74194 


1.25 


7443 


.87 


74125 


.54 


74195 


.89 


7444 


.87 


74126 


.63 


741% 


1.25 


7445 


.89 


74141 


1.04 


74197 


.89 


7446 


.93 


74145 


1.04 


74198 


1.79 


7447 


.89 


74150 


.97 


74199 


1.79 


7448 


1.04 


74151 


.79 


74200 


5.90 


7450 


.17 


74153 


.99 






LOW POWER TTL 






74L0O 


> .25 


74L51 


> .29 


75L90 


$1.49 


74L02 


.25 


74L55 


.33 


74L91 


1.45 


74L03 


.25 


741.71 


.25 


74L93 


1.69 


74L04 


.25 


74L72 


.39 


74L95 


1.69 


74L06 


.25 


74L73 


.49 


74198 


2.79 


74L10 


.25 


74L74 


.49 


74L164 


2.79 


74L20 


.33 


74178 


.79 


74L165 


2.79 


74130 


.33 


74L85 


1.25 






74L42 


1.49 


74L86 


.69 







HIGH SPEED TTL 



74H0O S .25 

74H01 .25 

74H04 .25 

74H08 .25 

7-IH10 .25 

74H11 .25 

74H20 .25 



74H21 
74H22 
74H30 
74H40 
74H50 
74H52 
74H53 



S .25 



8000 SERIES 



8091 
8092 
8095 
8121 
8123 
8130 
8200 
8210 



1.97 
2.33 
2.79 



8214 
8220 
8230 
8520 
8551 
8552 
8554 
8810 



S1.49 
1.49 
2.19 
1.16 
1.39 
2.19 
2.19 
.69 



9000 SERIES 



900'2 
9301 



$ .35 9309 
1.03 9312 



74H55 
74H60 
74H61 
74H62 
74H72 
74H74 
74H76 



8811 
8812 
8822 
8830 
8831 
8836 
8880 
8263 
8267 



9601 
9602 



S .25 
.25 



2.19 
2.19 
2.19 
.25 
1.19 
5.79 
2.59 



TTL 




7442 


$ .59 


7447 


.69 


7489 


1.99 


74153 


.69 


74193 


.99 




MEMORIES 



1702 A 


$14.95 


2101 


2.95 


2102-1 


3.25 


2102-2 


3.25 


5203 


12.95 


5260 


.99 


5261 


.99 


5262 


2.95 



DECEMBER SPECIALS 

9 DIGIT LED DISPLAY FNA 37 

On multiplexed substrate, comm. ca- 
thode compatable with all 8 digit 
calculator chips, 7 segment right hand 
decimal, red with clear magnifying lens, 
.12" character, 1 to 4 MA, 1.8 V typ 2 J /s" x 
>>" x '/"" high $3.95 



NINE DIGIT SPERRY 

GAS DISCHARGE DISPLAY 

SP-425-09 1.25" x 3" overall — .25" digits — connects 
to 18 led edge connector ■ — hi voltage — prime quality 
$1.49 

DVM CHIP 4V« DIGIT 

MM5330 — P channel device provides all logic for 4'/i 
digit digital volt meter 16 pin DIP with data $1 4.95 



LINEAR 




324 


$1.19 


380-8 


1.09 


565 


1.49 


739 


.89 


75491 


.59 


CLOCK 




CIRCUITS 


5311 


$3.95 


5312 


2.95 


5314 


3.95 


CALCULATOR 


CHIPS 




5001 


$1.49 


5002 


1.98 


5005 


2.49 



NEW ITEM - EXCLUSIVE WITH IEU 
RESISTOR ASSORTMENTS 

SUPPLIED WITH CONVENIENT STORAGE UNIT 
DESIGNED FOR EXPERIMENTERS, TECHNICIANS AND SCHOOLS 



RS1-25 $99.50 

AN ASSORTMENT OF 

2725 RESISTORS 
170 VALUES FROM 

.51 OHMS TO 5.6M OHMS 
QUANTITIES DETERMINED 

BY TYPICAL USAGE 
V, WATT 5% 

CARBON FILM 

+ $1.00 SHIPPING 
& HANDLING 
SHIPPING VIA UPS OR 
PARCEL POST 

REPLACEMENTS IMMEDIATELY 

AVAILABLE AT LOW COST 

BY MAIL FROM IEU 



Data sheets on request. With order add 
$.30 for items less than $1.00 ea. 



. ._„,.<.- 


y. * fc - v - C . 


v 


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v 


C t « t •» 


f i, ' fe «, « < 


i; 


« . * ■ * - 


%. < $ <' f c 9 i 


k. 


lifili 


f < • « $ > * *• 


6, 


*f MH 


• < <M * | f v 


6 


• « *« t« 


e*«*«ec«' 


fi 


• f « < if 


«M » e # < « i 


If 


• i « - • • 


$> •■ • * it < •< 


| 


• f ft. • * - 


tvf' <* \ * ■- 


fe. 


f < f < f { 


%':*'. %' ( *"- 


*>• 


25 $114.50 


RS 3-50 $69 


5C 



* 



Rohm 

QUALITY '■ RCLIABIUJY 



AN ASSORTMENT OF 

4000 RESISTORS 
100 EACH OF 40 

STANDARD VALUES 

1 OHM TO 3.3M OHM 
'/< WATT 5% 

CARBON FILM 



AN ASSORTMENT OF 

2000 RESISTORS 
50 EACH OF 40 

STANDARD VALUES 

1 OHM TO 3.3M OHMS 
V, WATT 5% 

CARBON FILM 



LEO'S 

MV10B 

MV50 

MV5020 



ME4 

MAN1 
MAN2 
MAN4 
MAN5 
MAN6 
MAN7 
MAN3 

MAN8 
MAN66 
MCT2 



Red TO 18 
Axial leads 
lumbo Vis. Red 
(Red Dome) 
lumbo Vis. Red 
(Clear Dome) 
Infra red diff. dome 
Red 7 seg. .270" 
Red alpha num .32" 
Red 7 seg. .190" 
Green 7 seg. .270" 
.6" high solid seg. 
Red 7 seg. .270" 
Red 7 seg. .127" 
straight pins 
Yellow 7 seg. .270" 
.6" high spaced seg. 
Opto-iso transistor 



.29 
3.45 
3.75 



MEMORIES 





1101 


.22 


1103 




1702A 


.22 




.54 


2102-2 


2.19 


5203 


4.39 


5260 


1.95 


5261 


3.45 


5262 


4.25 


7489 


1.19 


8223 




74200 



256 bit RAM MOS 
1024 bit RAM MOS 
2048 bit static PROM 
UV eras. 

1024 bit static RAM 
2048 bit UV eras PROM 
1024 bit RAM 
1024 bit RAM 
2048 bit RAM 
64 bit ROM TTL 
Programmable ROM 
256 bit RAM tri-state 



S 1.50 
3.95 

17.95 
4.25 

17.95 
2.49 
2.69 
5.95 
148 
3.69 
5.90 




MULTIPLE DISPLAYS 

NSN33 3 digit .12" red led 12 pin 

tits 1C skt. 

5 digit .11 led magn. lens 

com. cath 

4 digit .11 LED magn. 

lens comm. cath. 

9 digit 7 seg led RH 

dec clr. magn. lens 
SP-425-09 9 digit .25" neon direct 

interface with MOS/LSI, 

180 VDC. 7 seg. 



CALCULATOR » 
CLOCK CHIPS 



SHIFT REGISTERS 



1024 bit accum. (!■ 

mDIP 

500/512 bit dynarr 

QUAD 25 bit 



937 
944 
946 



949 
962 
963 




12 DIG 4 (unct fix dec 

Same as 5001 exc 

btry power 

12 DIG 4 fuel w/mem 

6 DIG 4 funct chain & dec 

18 pin 6 DIG 4 funct 

8 DIG 5 funct K & mem 

9 DIG 4 funct (btry sur) 
2B pin BCD 6 dig mux 
24 pin 1 pps BCD 

4 dig mux 

28 pin 1 pps BCD 

6 dig mux 

24 pin 6 dig mux 

40 pin alarm 4 dig 



2.79 
2.99 
1.98 
4.45 
5.35 
5.35 
4.45 



4.45 
4.45 
5.39 



Satisfaction guaranteed. Shipment will be made via lirst class mail in U.S., 
Canada and Mexico within 3 days from receipt ol order. Add $.50 to cover 
shipping and handling for orders under $25.00. Minimum order $5.00. 
California residents add sales tax. 



LINEAR CIRCUITS 

300 Pos V Reg (super 723) TO-5 $ .71 

301 Hi Perf Op Amp mDIP TO-5 .29 

302 Volt follower TO-5 .53 

304 Neg V Reg TO-5 .80 

305 Pos V Reg TO-5 .71 

307 Op AMP (super 741) mDIP TO-5 .26 

308 Mciro Pwr Op Amp mDIP TO-5 .69 
309K 5V 1A regulator TO-3 1.35 

310 V Follower Op Amp mDIP 1.07 

311 Hi perl V Comp mDIP TO-5 .95 

319 Hi Speed Dual Comp DIP 1.13 

320 Neg Reg 5.2, 12, 15 TO-3 1.19 
322 Precision Timer DIP 1.70 
324 Quad Op Amp DIP 1.52 
339 Quad Comparator DIP 1.58 
340K Pos V reg (5V, 6V, 8V, 12V, 

15V, 18V, 24V) TO-3 1.69 

340T Pos V reg (SV, 6V, 8V, 12V, 

15V, 18V, 24V) TO-220 1.49 

372 AF-IF Strip detector DIP 2.93 

373 AM/FM/SSB Strip DIP .53 

376 Pos V Reg mDIP 2.42 

377 2w Stereo amp DIP 1.16 

380 2w Audio Amp DIP 1.13 
380-8 .6w Audio Amp mDIP 1.52 

381 Lo Noise Dual preamp DIP 1.52 

382 Lo Noise Dual preamp DIP .71 
550 Prec V Reg DIP .89 
555 Timer mDIP .89 
556A Dual 55S Timer DIP 1.49 
560 Phase Locked Loop DIP 2.48 
562 Phase Locked Loop DIP 2.48 

565 Phase Locked Loop DIP TO-5 2.38 

566 Function Gen mDIP TO-5 2.25 

567 Tone Decoder mDIP 2.66 

709 Operational AMP TO-5 or DIP .26 

710 Hi Speed Volt Comp DIP .35 

711 Dual Difference Compar DIP .26 
723 V Reg DIP .62 
739 Dual Hi Perf Op Amp DIP 1.07 
741 Comp Op Amp mDIP TO-5 .32 

747 741 Dual Op Amp DIP or TO-5 .71 

748 Freq Ad] 741 mDIP .35 
1304 FM Mulpx Stereo Demod DIP 1.07 
1307 FM Mulpx Stereo Demod DIP .74 
1458 Dual Comp Op Amp mDIP .62 
1800 Stereo multiplexer DIP 2.48 
LH2111 Dual LM 211 V Comp DIP 1.70 
3900 Quad Amplifier DIP .35 
7524 Core Mem Sense AMPL DIP .71 
8038 Voltage conlr. osc. DIP 4.25 
8864 9 DIG Led Cath Drvr DIP 2.25 
75150 Dual Une Driver DIP 1.75 

75451 Dual Perepheral Driver mDIP .35 

75452 Dual Peripheral Driver mDIP .35 

75453 (351) Dual Periph Driver mDIP 35 

75491 Quad Seq Driver for LED DIP .71 

75492 Hex Digit driver DIP .80 



: 



< 



INTERNATIONAL ELECTRONICS UNLIMITED I 

g~ P.O. BOX 1708/ MONTEREY, CA. 93940 USA 
■naSP PHONE (408) 659-3171 










~ $599.00 



the pint size computer that does it all. 

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processors available. The system includes full keyboard 
control, status panel, 4K RAM*, Expandable Prom and 
rear panel connector access. Unit is completely assem- 
bled and tested in a compact, desk-top enclosure. 
"Additional RAM Available 




Options for Above: 

Cassette Interface (Includes 

Tape Program) 
Video Interface (R.F. or Video) 
Modem 

RS-232 Interface 
TTY Interface 
TTL Interface 
Parallel Interface 
Complete Video Display 

Assembly (Room for Floppy 

Disc) 
Floppy Disc 
Line Printer 
Tape Reader 
Export Version Available 
Note: All Above are Assembled 

and Tested. 



Send Cash or Check (MasterCharge or 
BankAmericard) with order to: 
SYSTEMS RESEARCH, INC. 

P.O. Box 151280 

Salt Lake City UT 841 1 5 

801-942-1093 

Add $ 5J30 for Postage and Handling. 

BankAmericard # 

Master Charge # 

Exp. Date 

Signature 




9080 Microproc $56.00 

Replaces 8080 

91 L02 1 K low power RAM 3.90 

2102 1k RAM 2.90 

ASCI I Keyboard Kit 79.50 

FEATURES: Full 55 key, reliable scanning logic, N 
key rollover, TTL compatible parallel output. Also 
available-serial output, parity bit, TTY current loop 
output. 



* 

Other 

kits available: 

1702 PROM Programmer 125.00 

8223 PROM Programmer 79.50 

Audio cassette interface 69.50 
CRT TV display 



Write for information on our INTELLIGENT TERMINAL 
and other computer products 




A| MIKRA-D Inc., 
P.O. Box 403, 
Holliston MA 01746 



compilers, stack, assembler, 
mnemonic, opcodes, 
disavowal. 

A uP could be used as the 
heart of an automatic 
bowling scorer, getting pinfall 
data, machine position data, 
bowler ID data and special 
information for error 
correction — and in turn 
would control the printer (or 
TV display) error correction 
display, etc. I have special 
interest in such a machine! A 
machine exists, implemented 
with IC logic — but what 
power has a u P ? 1 
Programming the uP must 
come after a good knowledge 
of its inner workings and a 
good mental model is 
developed. 

I hope BYTE magazine 
will try to get to the basics of 
computing using the uP. What 
jobs are they fitted to? Could 
an 8080 be used for: 

1 . A complex pin-ball 
machine control? 

2. A computer like HP-65? 

3. Bowling computer? 

4. Automatic machine 
controls — various. 

I hope your magazine will 
direct some effort towards 
people with needs and 
interests like mine. 

Pat Murphy 
Muskegon MI 



You should be 
straightened out on the 
circulation error by now, Pat. 
We've had some articles on 
basics lo date, and will 
continue to do so in future 
issues. 



LOGICAL 
COMPLEMENT 

Dear Mr. Helmers, 

I was struck by your 
editorial in the October 1975 
issue, "The Home Brew 
Voder," because I have long 
wanted to be able to use a 
small computer for exactly 
the opposite purpose. I want 
to be able to speak into a 
microphone and have an 
electric typewriter type out 
the words I am saying. 

I am a writer and, speaking 
as a writer, it has always been 
the most tedious (if 
necessary) chore when 



researching material to have 
to copy out my source 
material by hand, to make 
notes by hand, and then to 
rewrite my first drafts by 
hand (and by "hand" 1 mean 
by typewriter also). It would 
be much easier and more 
accurate when researching 
source material especially to 
be able to read the material 
out loud and have an accurate 
typescript made 
automatically, or, what 
amounts to the same thing, to 
read the material into a tape 
recorder for later 
transcription . . . 

... If you or any of your 
readers can convert this idea 
of mine into practical 
circuits, I would certainly 
appreciate it, and I am sure 
the idea is commercially 
viable as well. 

M. Krieger 

37 Eighth Ave. 

Brooklyn NY 11217 



THE AUDIO CASSETTE 
TOWER OF BABEL 

Dear Mr. Helmers, 

Congratulations! I am glad 
to see a real magazine 
exclusively devoted to the 
"do it yourself" computer 
enthusiast — now 1 don't have 
to buy an audio or electronic 
magazine for one article 
about computers. 

You are right about the 
three areas to cover — 
hardware, software and 
applications. However, there 
is another area that ties these 
three together and without it 
we would have chaos — that 
area is standards! 

Now that so many 
manufacturers are getting 
into tne computer field 
everyone wants to do their 
own thing. That's fine - but, 
we do need standards. It is 
not really important what 
goes on in the "black box" or 
how fancy the operating 
system is as long as we can 
swap programs and they will 
run without having to rewrite 
them. 

As the first magazine in 
the field, you can be the 
driving force in helping to 
prevent a "Tower of Babel." 
We need a specification 
spread sheet so that 



104 



(TeH 7400N TTL *m 



SNMdUN 
5N7401N 
SN7402N 
SH7403N 

SNM04N 

SN7405N 

SN74Q6N 
SN/40/N 
SN7408N 
SNM09N 
SIMM ION 
SNMIIN 
SN/4I2N 
SN74I3N 
SN7414N 
SN/416N 
SN74I7N 
SN7JI8N 
SN/420N 
SNM71N 
SNM73N 
SN/475N 
SNM2BN 
SNM2/N 
SN/*29N 

sn;«on 

SN7432N 
SN7437N 
SNM3BN 
SNM3HA 
SN7440N 
SN7441N 
SN/442N 
SN7443N 
SN7444N 
SN7445N 
SN7446N 
SN/447N 
SNM4BM 
SN/45UN 



SN7451N 

SN7453N 

SN7454N 

SN7459A 

SN746DN 

SN74 7QN 

SN7472N 

SN7473N 

SN7474N 

SN7475N 

SN747fiN 

SN7488N 

SN7-182N 

SN/483N 

SN7485N 

SN/486N 

SN7488N 

SN7489N 

SN7490N 

SN7491N 

5N/492N 

SN7493N 

SN/494N 

5N7495N 

SN7J96M 

SN 741 OON 

SN74107N 49 

SN74I2IN 55 

SN74122N 49 

SN741Z3N l.Ob 

SN74125W 60 

SN74I26N 81 

SN74132N 3 0(1 

SN74I41N 1 lb 

SN74142N bbll 

SN74I43N 7 0(1 

SN74144N 7 0(1 
I SN74I45N 1 lb 

I SN74148N 750 

SN7415QN 1 III 
i Discount for I Oil Cmulii 



SN/4151N 
SN741'jjN 
SN 7-1 1 'j'IJM 



125 



SN74155N 1 21 
SN 74 lb UN 
SN74157M 
SM741GON 
SN 74 16 IN 
SN74163N 
SN741G4N 
SN741F.5N 
SN74166N 
SN74167N 
SN74170N 
SN/4I/7N 18.00 
SN/4I/3M 1.70 
SN74174N I 9b 
SN74175N 1.95 
SN74176N 90 
SN7417 7N 90 
SN74180N 1,05 
SN711H1N 3.5b 
SN74182N 
SN74184N 
SN74 185N 
SN7418/IJ 
SN74I90N 
SN7419HJ 
SN74192fJ 
SN74193N 
SN74191N 
SN74195PI 
SN7419EH 
SN74I97N 
SN7419HN 
SN74I9UN 
SN74700N 
SN74251N 
SN74ZB4N 
SN74286N 
nil 7400s 



3 00 



2.30 
2 70 
Ei.00 



I SO 



1 00 



2 25 
2 25 
7 00 
2 50 
600 
6.00 



LU40U0 
CD400I 
CU40U2 
CU40(lli 
CD4007 
CD4009 
CUIQIll 
UD4CJ1 1 
CU40I2 
CU4UI3 
C04U16 
C0401? 
CU4019 
CIJ4070 
LD4022 
CU4023 
C 04 074 
C04025 
CU4027 
CU4028 
ril4(l79 



CMOS 



CO4030 

CO4035 
CD4040 
CD4042 
CD4044 
CD404G 
C 1)404 1 
C 04 049 
CU4Q50 
CD4051 
CU4Q53 
CIMQGO 
CD40G6 
C 04069 
CD4071 
CU40SI 
74COON 
74C02N 
74 COIN 



MC1UN 

74C70N 

/4C30N 

74C47N 

74C73N 

74C74 

74C90N 

74C96N 

74C107N 

74Clb1 

74C154 

74C157 

74C1GO 

74CI61 

74C163 

74C164 

74C173 

74C193 

74C 19b 

BOC97 



LMI 



15.00 

2 5U 

3 75 



LINEAR 



IM712H 7 00 

LM300H BO 

LM301H 3/100 

LM301CN 3.' 1.00 

LM302H 7b 

LM3Q4H 1 00 

LM305H 95 

LM307CN 3b 

LU308H 1.00 

LM30BCN 1.00 

LM309H 1.10 

IM309K 1 2b 

LM310CN 1 15 
LM311 



IM311N 



90 



9 00 



50 



LM'ilHLN 
1.M319N 
LM319U 
LU32IIK 5 I 35 
IU320K5 2 1 3b 
LMJ70K 12 1 3b 
LM370K 15 1 3b 
I.M323K! 
LH324N I Hll 
LM339N I 70 
IM3'10K5 195 
LM340K 17 I 95 
LM340K lb 1 95 
LM34UK 24 1 95 
LM3401ub 1 7b 
LM340TnG 1.75 
LM340In 12 1 75 
LM340TO 15 I 75 
lM3407o74 1 75 
LU350N 1 00 
LM35ICN 65 
LM370N I 15 
1M370H 1 IS 



LM373N 
LM377N 
LM380N 
IM380CN 
LM381N 
LM382N 
NE!i01K 
NE510A 
NE531H 
NE536T 
NE54QL 
NEbbGN 
NE553 
NE555V 
NEbBbH 
NE565N 
NE5GGCN 
NE5G7H 
NES67V 
LM703CN 
LM709H 29 

LM709N 29 

LM710N 79 

LM711N 39 

LM723N .55 

LM723H 5b 

LM733N 1 00 
LM739N 1.29 
LM741CH 3 1 00 
LM741CN 3 1 00 
LM741 14N 39 
LM747H 79 

LM747N 79 

LM748H 39 

LM74BN 39 

LM13D3N 90 
IMI304W 1 19 
LMI305N 140 
I.M1307N Kb 



4 00 
1 39 
105 
1 79 

1 79 

soo 

GOO 
3 00 
GOO 
GOO 
79 

2 50 
.49 
.99 

1.25 
1.S5 
1.25 
1.50 



LM1310N 2.9 

LM1351N 1G 

LM14I4N 1 7 

LM1458C G 

LM 149GN 9 

LMlbbGV 18 

LM2111N 1.9 

LM7901N 2 9 

LM30B5H G 

LM39UUN G 

LM3905N G 

LMS556N 1 8 

MC5558V l 

LM7b?bN 9 

LM7578N 7 7 

LM7534N 7 2 

LM7535N 1 2 

8038B 4 9 

LM75450 4 

75451CN 3 

754b2CN 3 

754b3CN 3 

75454CW 3 

75491CN 7 

75492CN B 

75494CN B 
RCA LINEAR 

CA3G13 1 / 

CA3023 2 1 

CA303b 2 2 

CA3039 1 3 

CA3046 I 1 

CA3059 2.4 

CA30GO 2.8 

CA3080 .8 

CA3Q83 I G 

CA3086 -5 

CA3089 3 1 

CA3091 8 2 

CA3173 IB 

CA3G00 17 



DATA HANDBOOKS 



Pm-out 6 Description of 5400/7400 ICS S2.95 
Descfiplion of 4000 Series ICS $2.95 

S2.95 



7400 
CMOS 

LINEAR Pinout & Functional Description of 
Linear Circuit: 



6' POWER SUPPLY CORDS 

^^ ^CONDUCTORS SPECIAL 

^P^"™" 3/S1.00 



THUMBWHEEL SWITCHES 

j(^l TrillMHmilLl nviTClt QtiLY 



5! DP | [i...,>, .■■„.,'i."i,t.| ; tg 



JAMES CHRISTMAS SPECIALS 



DIODES 

IN4U0I bOVisM Ainji lb-Si 

IN4D02 lOOVL-i I Amp 15 SI 

IN4003 200V I'M Amp 15 SI 

Il\41ia4 400V ,-- I Amp 15 SI 

IN4148 Sivtliliinij 2U SI 

TRANSISTORS 

7N7y07APNPSwili:linui BSl.O 

7l\l7222ANPNSwi.cli.ini G'Sl.O 

7N3904 NPN Amp G'SI.O 

7N390G PNPAmp C-S1 

7M918 IVPNRF 6 SI 

7N5951 NJFi-t CSI.O 

C10BB1 3.6AintiSCR 2'S1 



TTL/LINEAR 

74110 Gjle 7/SI0 

7447 Decoder, 7 

7490 Cuumei 4 

74100 SBilLJtrii .9 

74154 Decodei .9 

74197 Countll 7 

LMJOIH-LM741H 4/SI Q 

LM324N-Quail 741 1 I 

LH309H 5V R«g 10 5 .7 

LM303K 5V Reij to 3 .9 

MM5262 DYNAMIC 
2KRAM $2.95 



CLOCKS. CALC. CHIPS 



MM53HN 
MM5312N 
MM53I3N 
MM6314N 

MMS31GM 

MM5725N 
MM5736N 
MM5738N 



4 Diyil 
G Digit 
6 Digit 
G D.yil AUr ii 
8 Dign-4 Fui 
G Digit 4 Fui 
B Digit 5 Fin 



S2.95 
2J5 
2.95 
255 

3.95 

1.B5 

. 1.9S 

. 2.95 



26 Awg RIBBON CABLE 
1 F t. Minimum 1 9 ft. 10 It. 

.79 11. .2511. 

.59 It. .49 It. 

.89 ti. .79 ft. 



32 C 



.89 (t. 



1.G9 1I. 



C/GITflirUDLT^IETER 



JEflQi 




GENERAL DESCRIPTION 



$39.99 Per Kit 



SINGLE UNIT 



Tilt; JE801 is a three and one half digit, auto 
polarity digital voltmeter, in a kit form. It 
features several options not available in any 
commercial digital voltmeter. Us low cost is 
perhaps the most important feature, which is 
achieved by olferinij It in a kit form. A kit 
allows the unit lo be used by small OEM's 
where cost effect tveness is an important factor, 



ami by the hobbyist who has to be concerned 
with cost. The unit also features on card 
regulators, allowing it to be operated ofl a 
single plus and minus fifteen volt, unregulated 
power supply. The unit has a small size of 
three inches width, three and three quarters 
of an inch length, and one and a quarter inch 
height. 



FND70 
MAN 1 
MAN 2 
MAN 3 
MAN 4 
MAN 7 
DL33 
DL747 



DISPLAY LEDS 

Com. Caih. .250 

Com. Ano. .270 S 

5x7M.ilmc .300 

Com. Catlt. .125 

Com. Cath. .187 

Com. Ano, .30 

Com. Callt. ,12b 

Com. Ano. .625 



a 



DISCRETE LEDS 



MV 10 
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MV 5024 
MV 5074 
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RESISTOR ASSORTMENTS SI. 75 per assort. 

contains 50 pcj. of % watt. 5V ibu'sidis 
10 OHM- 12 0HM- 15 OHM- 18 OHM- 22 OHM 
27 OHM- 33 OHM 39 OHM- 47 OHM- 5G OHM 
G8 OHM- 82 OHM 100 OHM-120-OHM-15O OHM 
1B0 OHM 720 OHM 270 OHM 330 0HM-39D OHM 
170 OHM-5G0 OHM-680 OHM-870 OHM 



; 1.2K 
3.3K 



33K 



180K 
470K 
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I00K 
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ASSORTMENTS S9.95 

Each assortment cuntains 14 pes nl 10 turn pats. 
ASST.A 2ei: 10 OHM-20 OHM-50 OHM-1G0 OHM 

200 OHM-250 OHM 500 OHM 
ASST.B 2m: IK, 2K, 2.5K, 10K, 20K. 2bK, 50K 
ASST. C 2 Da: 5DK. 100K, 200K, 250K, 500K, 1M, 



All | 



2M 

oitutilu 






in tit 



. S.99 ea. 



DPST C&KROCKERSWITCH 

They arc rated at 125 Vac <°> 5A. 
They ate excellent in application 
such as Microcomputer 
Panel Switches (fcn cq 

Dim: 1"x1"x'/«" 



PRIME 

INTEGRATED flSsr g 
CIRCUIT 
ASSORTMENTS i:; 

ASS 7 I 



C4001 tO07 

CD4QIE 4011 
LM30II 301N 



Satisfaction Guaranteed. $5.00 Min. Order. U.S. Funds. 

California Residents — Add 6% Sales Tax 

Write for FREE 1976 Catalog - Data Sheets .254 each 

M7VSS 

P.O. BOX 822, BELMONT, CA. 94002 
PHONE ORDERS - (415) 592-8097 



MICROPROCESSOR COMPONENTS 
8008 - $19.95 2102 $2.95 



B223 


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57030 


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74S287 


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91L02 



IK Sum: RAM Dlieci licplac 



Clot General Purpose Logic CARD Board 14. 

eiy High Noise Immunity ' Holds 12 ea. 14 pin DIPS 
4 pin Edge Connection 



THE KILOBYTE RAM CARG 
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HIGH QUALITY 
PB. TYPES .69 



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XR2206KA SPECIAL $17.95 

Includes monolithic function neneialot IC, PCboatd.and assembly 
instruction manual. 

XR2206KB SPECIAL $27.95 

Same as XR22Q6KA uliuve and includes external components 
for PC hoard. 



TIMERS 

XR-555CP SPECIAL 

XR-320P 

XR-55BCP 
XR-255GCP 
XR-2240CP SPECIAL 

PHASE LOCKED LOOPS 
XR 210 

XR-215 

XR-567CP 
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1194 



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LOI10/1 II UVM Clii|iSet 

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MC140RI.7 A/U 

F334) FIFO 



8Z63 
87G7 
B?BB 
882G 



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TYPE VOLTS 

IN74G 3.3 

IN751A 5.1 

IN752 5.6 

IM ?53 G? 

IN754 6.8 

IN965B 15 

IN5232 5.6 

IN5234 6.2 

IN5235 6.8 

IN5236 7 5 

IN456 25 

114458 150 

IN485A IfiO 

INrtOOl 50PIV 

IN4U0! I00PIV 



TYPE VOLTS W 

IN4003 200 PIV I AMP 
JN4004 400 PIV 1 AMP 



I/I Dl) IN3GQ0 



4/1 00 
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IN4148 
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IN4734 
IN4735 
IN4736 
IN4738 
IN474? 
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1w 



35 AMP 
100 PIV 35 AMP 
1186 200 PIV 35 AMP 
IN 1 188 400PIV 35AMP 



MPS A05 5 1 00 



MPS A0f> 

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FN2415 

7N2484 

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2mm 

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IS 100 



TRANSISTORS 

PN3SC7 3S1.00 

msblii 4SI.O0 

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mms 

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47 pi 
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(kit) 




DIRECTLY COMPATIBLE WITH ALTAI R 
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FEATURES: 

• to 300 character per second bi-directional 
reading speeds. 

• Single 5 volt, 2 amp power requirement. 

• Reads any one inch, 8 level paper tape. 

• Reads any tape material with less than 60% 
transmissivity (oiled yellow paper). 

• Stepper motor drive - one moving part. 

• Spring loaded line filament lamp with 
15,000 hour life. 

• Self-cleaning read head. 

• TTL interface, mates with most micro 
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• Mounts in 4-3/8"H x 4-1/4"W panel cutout 
extends 2-1/2" behind and in front of 
the panel. 

PRICES: 

• Fly Reader 30 Kit (only main PC $295 
board requires assembly) 

• Fly Reader 30 (assembled and tested) $365 

• Optional fan fold trays (200' 
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rack panel $1 10 

• Optional 19"Wx5-1/4"H rack panel 
mounting $ 25 

• Optional 5/8 level tape gate for 
reading both 5 and 8 level tapes $ 25 

TERMS: 

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• Cash with order or master charge plus $3 
shipping for individuals within continental 



U.S.A. 



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TELETERMINAL CORPORATION 

IE CAMBPIDGESTBEET 

BUHLINGTON, MASSACHUSETTS 01B03 

617/a72'85DU 



comparison can be made. For 
example, Popular Electronics 
came out with their HIT 
cassette interface, the 
Computer Hob by 1st has 
another, the Southern 
California Computer Society 
has one and so does MITS. I 
understand that the Digital 
Group in Denver has a tape 
transport. Which is best? 

Can I run MITS BASIC in 
any other mini? Does anyone 
make a mini I can run 
Datapoint software in? 

I realize that this is quite 
an undertaking but think of 
the thousands of hours that 
will be saved if this 
information is available. You 
have made a good start with 
"Which Microprocessor for 
You?" 

As you probably guessed I 
am an application man and 
over the years have developed 
quite a Fortran subroutine 
library. This makes it easy to 
write a program — just call, 
call, call! I hope to provide 
some useful articles later after 
I get my Altair up to being a 
workhorse instead of just a 
toy. 

William D. Roch 
Woodland Hills CA 



ON LIFE 

AND 
LIFELINE 

Dear Sirs: 

The first issue of BYTE is 
excellent. BYTE looks as if it 
is going to be exactly what 
(in my opinion at least) a 
computer hobbyist magazine 
ought to be. 

Just one slight correction; 
the inventor of the game of 
LIFE is John Horton 
Conway, a professor of 
mathematics at Cambridge 
University (England), not 
Charles Conway as reported. 
LIFE was first widely 
publicized in the October 
1970 issue of Scientific 
A merican and according to 
Martin Gardner in the 
November 1971 issue of that 
periodical (page 121), a 
newsletter called LIFELINE 
was started in 1971 by 
Robert T. Wainright, 1280 
Edcris Rd., Yorktown 
Heights NY 10598. However, 
I never subscribed to the 



newsletter and have no idea 
whether it is still going or 
not. Perhaps one of your 
other readers will be more 
informative . . . 

Charles A. Dunning Jr. 
Sterling Heights MI 

1 AND 1 
EQUALS 2? 

BYTE: 

An article in issue #2 
prompts me to write about 
something: Have just started 
reading up on computers and 
associated equipment. One 
item 1 read was about AND 
gates and OR gates, and their 
logic. In my opinion they are 
designated incorrectly. 
Remember in grade school, 
when you had the arithmetic 
problem 1 + 1=2? 

Most of us said "1 and 1 
equals 2." In other words the 
+ sign (plus sign) stood for 
and. 

Now in Boolean logic they 
say that the + sign means OR. 
And the • means AND. 

Would have been much 
better to have the + sign 
mean AND, and the ■ sign 
mean OR (the • sign looks 
more like the or OR filled 
in than a plus sign), but it's 
too late to change this 
system, because it's been in 
use too long. 

But maybe it's not too late 
to change the system used on 
page 43 of issue #2 of BYTE. 
This shows LED bit pattern: 
0-LED on; t-LED off. To me, 
the filled in zero looks more 
like an LED that is on, and it 
seems a better illustration 
would be: »-LED on; 0-LED 
off. 

The ASCII code for A 
would then look like this: • 
000 00« with the filled-in 
circles indicating the punched 
out holes. 

BYTE looks great. Keep it 
up! 

James C. Madsen 
Fresno CA 

The AND function is 
"logical product, " the OR 
function is "logical sum. " 
The symbols are of course 
merely the usual product and 
sum symbols of mathematics. 
The way it is said in grade 
school is colloquial but, 
unfortunately, not true. 



106 



THE SUNTRONIX MODEL KBD IV Keyboard is ideally suited as a general 
purpose ASCII Keyboard for data terminal applications. This keyboard more than 
meets the needs of the data entry market for long life and reliability. 

The KBD IV utilizes the 2 key rollover solid state read-only MOS memory allowing 
encoded outputs to be strobed out as each key is depressed. A second key may be 
depressed concurrent with the first, but the second key encoded output will not be 
strobed out until the first key is released. This feature prevents ambiguity of 
character codes as a result of two keys being depressed in rapid succession. 

ELECTRICAL SPECIFICATIONS: 

* Voltage requirements — +5.0 V and —12.0 V 

* Power consumption — less than 200 mw 

* Outputs - standard ASCI I; 8-bits + strobe 

* Negative or positive logic output, jumper selectable 

* Output connector — standard 14 pin DIP IC socket 

MECHANICAL FEATURES: 
*Size- 1 2%" x 6%" x 2 1 / 2 " 

* High grade glass epoxy PC board 

* Keyboard ROM SMC KR2376 40 pin MOS 

* Electronic shift lock, not mechanical 

* Keyswitches one integral assembly, not individual keys 

* Switches have four-finger phosphor bronze contacts with gold inlay 

* Keycaps are 2-shot high strength ABS plastic 

These keyboards are available off the shelf in two forms — fully assembled and 
unconditionally warranteed against defects in manufacture or materials for a full 
ninety days, or in the more economical kit version. Kit parts are fully warranteed 
against defects in manufacture or materials for a full ninety days. In either version, 
full instructions are supplied for operation, including specifications and data sheets. 
In the kit version, complete instructions are supplied for the assembly process. A 
reasonably competent technician can completely assemble and test this keyboard in 
one evening. All parts needed are included. 



INTRODUCTORY PRICES 

Factory assembled — $59.95 ppd. 
Complete kit, w/instructions — $54.95 ppd. 
Please add $1 .00 handling per order. 
Minimum order — $5.00 





SWmiUM mm 



UVI 



6 KING RICHARD DRIVE, LONDONDERRY, N. H- 03053 
603-434- 4644 




BOOK 
REVIEWS 



The Bugbook III: Micro 
Computer Interfacing by 
David G. Larsen, Peter R. 
Rony and Jonathan A. Titus. 
Published by E & L 
Instruments, Inc., 61 First 
St., Derby CT 06418; 
1-203-735-8774. $14.95. 

This excellent book is 
highly recommended to all 
microcomputer 
experimenters, and is a 
"must" for 8080 users. It 
includes probably the best 
available tutorial discussion 
of hardware and software 
techniques for interfacing 
microprocessors to external 
devices, enabling them to act 
as device controllers or 
sequencers. It also includes an 
excellent introduction to 
programming concepts and 
the 8080 instruction set, and 
a very good discussion of 
interrupt handling. 

Bugbook III is the fourth 
in a series of books prepared 
by the authors to teach the 
application of modern digital 
electronics to the control and 
monitoring of physical 
processes. Bugbooks I and // 
describe experiments with 
conventional TTL integrated 
circuits, while Bugbook IIA 
deals with asynchronous data 
communications using 
UARTs. Each of the 
Bugbooks describes 
experiments which are to be 
performed with the Micro 
Designer student-oriented 
interfacing system and the 



Mark 80 microcomputer, 
which arc marketed by E & L 
Instruments, Inc. Authors 
Larsen and Rony are 
associated with Virginia 
Polytechnic Institute and 
State University, where they 
teach both regular and 
extension courses on digital 
electronics. 

Bugbook III is organized 
into eight instructional units. 
Each unit begins with an 
introduction, a list of 
objectives, a glossary of 
definitions, and ends with a 
set of experiments, a test, and 
a review section which relates 
the material just covered to 
the initial list of objectives. 

Unit 1 provides a general 
introduction and orientation 
to computers and 
microprocessors, discusses the 
basic tasks of interfacing a 
microprocessor to the outside 
world, and summarizes the 
characteristics of the 8080 
microproccesor. Unit 2 
describes breadboarding 
techniques specific to the 
Mark 80 microcomputer 
system. Unit 3 introduces the 
basic concepts of stored 
programs, instructions, and 
machine language, explains 
how instructions are decoded, 
and summarizes the 8080 
instruction set in various 
ways. 

Unit 4 describes ways of 
generating device select pulses 
to signal one of several 
input/output devices, and 
relates the 8080's 
input/output instructions to 
the device selection signals on 
the address lines. Unit 5 
explains how microprocessor 
programs and timing loops 
can be used to provide time 
delays and sequencing for 
external control. Unit 6 is a 
lion-hearted attempt to 
clarify the complex details of 
decoding the 8080's external 
status signals in order to 
identify specific machine 
cycles which are entered as 
each instruction is executed. 

Unit 7 further develops 
the techniques for 
input/output, and describes 



how the Mark 80 bus signals 
and control lines may be 
monitored (the Mark 80 'is 
especially well designed for 
this purpose). Unit 8 
discusses subroutines, 
interrupts, external flags and 
stacks, and includes a good 
introduction to the possible 
ways of dealing with 
interrupts. 

The authors have done a 
really excellent job in several 
areas. One area is the 
definition of terms: Each unit 
begins with a glossary of 
definitions, and many 
definitions are repeated for 
emphasis in the context of 
the discussion in the text. 
Another area is the 
organization of the text for 
instructional purposes and 
the effort to provide 
motivation for the student. 
Still another area where the 
book succeeds is in the 
relation of hardware 
functions to software 
concepts. 

The material on the use of 
software timing loops and 
their use in sequencing and 
controlling external devices is 
difficult to find elsewhere. 
The discussion of interrupts 
covers the essential concepts 
of saving status information, 



the 
BUGBOOK' m 

\l I MICROCOMPUTER INTERFACING 

jj. If E*p«Hwn]! M I I'll' MARK 60* 

UKteCWlWUt* .i" H'.iBU SysriT" 



0HOr.RAI.1MMS 



33 




enabling and disabling the 
interrupt system, and 
choosing among interrupts of 
different priorities. 



The book does a good job 
of introducing basic 
programming concepts, and 
provides a large number of 
programming exercises which 
explore the 8080 instruction 
set in some depth. However, 
this Bugbook does not cover 
"higher-level" software 
concepts beyond the idea of 
simple loops and subroutines. 
All of the examples are 
presented in absolute 
machine language, and the 
use of assembly language is 
mentioned only briefly. 
There is no coverage of 
higher-level languages or of 
software "multi-tasking" 
approaches to the handling of 
multiple I/O devices and data 
streams. Perhaps these topics 
will be covered in another 
Bugbook. 

This book fills an 
i mportant gap in the 
currently available literature 
on microcomputers: It deals 
squarely with the 
interrelationships of hardware 
and software at the level of 
input/output device 
interfacing. This is in line 
with the authors' view of the 
role of microprocessors as 
device controllers rather than 
as general purpose computers. 
Readers who intend to 
connect their home computer 
system to their ham radio 
gear, model train system, 
electric range, burglar alarm 
system, or whatever, would 
do well to obtain this book. 
Any 8080 user who is a 
hardware or software hacker 
and is having trouble 
understanding the jargon of 
the "other side" would also 
profit from this book. The 
experiments depend to some 
degree on the layout of the 
Mark 80 system, but the text 
(with the exception of Unit 
2) is applicable to all 8080 
systems. For instructional 
purposes, this book is one of 
the best available on the 
market today. -d.h.f. 



Bugbook, Micro Designer and 
Mark 80 are trademarks of E & L 
Instruments, Inc. 



108 



OEQBB 




molded double-shot keys in red, white, 
keys in addition to letters, numbers, & 
are arranged in 4 rows, but are easily re 
positions. This makes for a very versati 
and type of key can be arranged in any 
Any type of encoding can be wired. Fi 

STOCK NO. B6015 Keyboard Kit 



KEYBOARD KIT 

This very unusual key- 
board kit is made by Micro 
Switch. It has a set of 
switches & space bar in a 
modular frame, plus 42 
or blue. There are 8 control 
many symbols. The switches 
moved or moved to other 
le keyboard, since any number 
pattern to suit your own needs, 
nished size is 9%" x 3%" x 2". 

2V 2 lbs. $1 9.95 ea, 2/35.00 



VOLTAGE REGULATORS 





B5169 



B5169 is a board containing 3 15 volt high current regulators 
with 0.1% regulation. 2 of the regulators are rated @ 3 Amps., 
and the other @ 6.0 amps. The current in each regulator may 
be doubled with the regulation going to 0.5%. All 3 regulators 
are short circuit proof, an.; 2 have electronic crowbar protect- 
ion. Brand new, in factory boxes. With data. 
STOCK NO. B5 169 $11.95 ea. 2/21.00 

B9013 is a triple regulator with ±12 volt regulation @ 200 ma., 
and the third regulator is a tracking regulator. It may be set 
between and 5 volts @ 500 ma. With data. 
STOCK NO. B9013 $5.95 each, 2/10.00 

B4481 is a VOLTAGE REGULATOR IC, type Ml 568. It is 
designed to provide balanced + and — output voltages at currents 
to 100 ma. each. It is set internally for ±15 volts but may be 
externally adjusted between 8 and 20 volts (tracking). Packaged 
in a 14 pin plastic DIP. With data. 
STOCK NO. B4481 ±15 volt regulator DIP $1.50 ea, 4/5.00 



COMPUTER DATA INPUT KEYBOARDS 




ASCII encoded keyboard. In its own enclosure. Originaly used in 
SANDERS ASSOCIATES 720 Terminal System. In like new 
condition. Usefull for any project requiring an ASCII encoded 
keyboard. 50 Alpha Numeric keys plus 1 1 computer symbols 
STOCK NO.B5283 keyboard $35.00 2/65.00 

MICRO-SWITCH (Honeywell) 8 bit binary coded board. 56 keys, 
alpha - meric and computer symbols Built in TTL decoder. New 
in factory cartons. A beautiful keyboard. 
STOCK NO.B5199 Microswitch keyboard. $45.00 2/80.00 



KEYTOPS & SWITCHES 
TO MAKE YOUR OWN KEYBOARD 




We have a large selection of KEYTOPS and SWITCHES, made by 
RAYTHEON CO. The keytops come in black, grey anil while, 
with contrasting legends. The switches mate with (he tops, and are 
magnetic reed switches. The following combinations are available: 
54 key typewriter set, keys only, black K9276 2.95 

54 key typewriter set, keys only, grey K9278 2.95 

54 key TTY set, no symbols white K9279 2.95 

54 key TTY set, with symbols white K9282 2.95 

54 key set, keys Si switches black K9288 30.00 

54 key set, keys & switches grey K9290 30.00 

54 TTY set, no symbols keys Si Sw. White K9291 30.00 

54 TTY set, with symbols, keys & Sw. whiteK9291 30.00 



1 1 Key Numeric set. Keys only Black 

1 1 Key Numeric set. Keys only Grey 

I 1 Key Numeric set, Keys only White 

12 Key numeric set. Keys only white 

I I Key Num.set, keys & switches Black 
1 1 Key Num. set, keys 8i switchesGrey 

1 1 Key Num. set, keys & switchesWhite 

12 Key Num. set, keys 8i switches white 



K9283 
K9284 
K9295 
K9286 

K9293 
K9294 
K9295 
K9296 



1.50 
1.50 
1.50 
1.50 

7.00 
7.00 
7.00 
7.50 



Blank key 1 14 keys wide 
Blank key 2 keys wide 
K9297A with switch 
K9297B with switch 



white 
white 
white 
white 



K9297A 3/.25 

K9297B 3/. 25 

K9298A 3/2.00 

K9298B 3/2.00 



TRANSFORMERS 

Cumputer projects need power supplies. Finding the right power 
transformer can be a problem. We have one of the largest and 
most diversified stocks of power transformers in the country. 
Below we list some representative items in our inventory. Our 
catalog, free on request lis ts many more. 



3d V. <"> 1.0 A. r.l, Ni G.3 V (<a 200 ma. 3 lbs. 
70 V. ("l 1.5 A. ct, 8i 6.3 V Cnl 500 ma. 6 lb. 
90 V. (a 2.0 A. ct, 8i 6.3 V <p> 1.5 A. 854 lb. 
50 V. @> 1.5 A. ct. Si 6.3V (iB500 ma. 6 lb. 
26 V. @ 1.0 A. ct. 8i6.3 V. <ip 500 ma. 3 lb. 
38 V. @ 1.5 A. ct. Si 6.0 V.@ 500 ma. 2 lb. 
350 V. @> 35 ma. ct. 8i 6.3 V. @> 2.7 A 2 lb. 
70 V. @> 1.5 A. ct. Si 6.3 V @ 1.5 A. 7Lb. 
35 V. <°> 6.0 Ct. Si 10 V. @> 10.0 A. 6.0 Lb. 
64 or 32 V. S> 8.0 A. ct. 8i 18 V. @ 8.0 A ct 



B9313 
B9314 
B9315 
B9316 
B9318 
B9319 
B9321 
B9322 
B9906 



3 50 2/6.00 
6.50 2/12.00 
9.95 2/19.00 
6.50 2/12.00 
3.75 2/7.00 
6.95 2/13.00 
3.50 2/6.00 
6.75 2/13.00 
8.95 ea. 



10 lb. B9905 1 1.95 



COMPUTER GRADE ELECTROLYTICS 

We carry a good selection of capacitors of all types, dipped micas, 
ceramic disks, mica trimmers, tantalums, silvered micas, tubulars, 
small electrolytics, high voltage, etc. Listed below are a few of our 
large computer grade electrolytic capacitors. 
VOLT MFD STOCK PRICE 



10v 
lOv 
10v 
15v 
25v 
35v 
50v 
75v 
200v 



40,000 

90,000 

160,000 

110,000 

32,000 

40,000 

10,000 

6,000 

500 



B2026 
B2495 
B2515 
B2352 
B2492 
B2255 
B2493 
B2450 
B2345 



2.00 each, 
3.00 each, 
3.25 each, 
3.50 each, 
3.00 each, 
3.50 each, 
3.25 each, 
3.50 each, 
2.50 each. 



6/11.00 

3/8.00 

4/12.00 

3/9.00 

4/10.00 

3/9.00 

4/12.00 

4/12.00 

4/9.00 



709 

47 09 

741 

747 

741 

747CT 

1458 



O P 

DESCRIPTION 

Hi Performance 

Dual 709 

Hi Performance 

Dual 741 

Hi Performance 

Dual 741 

Dual 741 



AMPS 

CASE STOCK 



PRICE 



TO-5 



B4301 



DIP B5301 

DIP B4316 

DIP B4317 

Mini DIP B4345 
TO-5 B3111 

Mini DIP B31 12 



.50 

1.00 

.65 

1.25 

.65 

1.25 

1.25 



5/2.00 
6/5.00 

5/3.00 
5/5.00 

5/3.00 
5/5.00 
5/5.00 



A 



DELTA ELECTRONICS CO. 

BOX 1, LYNN, MASSACHUSETTS 01903 
Phone (61 7) 388-4705 



MINIMUM ORDER $5.00. Include sufficient postage, excess 
refunded. Send for new 88 page Catalog 1 5, bigger than ever. 

fSBi BANKAMERICARD and MASTERCHARGE 
j*^J"d now accepted, minimum charge $15.00. Please 
OS include all numbers. Phone orders accepted. 



109 



RETAILING? 



BYTE Magazine is very new. And judging by the response 
from retail outlets that want to sell BYTE, we're sure it has 
a grand and glorious future. 

If you own or know of a friend who owns a retail store 
(electronic parts, radio-TV., hobby store, newsstand, 
student book store) we'd be more than happy to rush them 
our BYTE retail order form. 

We offer an extremely attractive discount, an unbeatable 
returns policy, and the only magazine for the serious 
computer hobbyist. More information? 

Write: 

BYTE Magazine 

Retail Sales Dept. 

Green Publishing, Inc. 

Peterborough, N. H. 03458 



BYTE FOR RESALE 




Discovering BASIC - A 
Problem Solving Approach by 
Robert E. Smith, Hayden 
Publishing Co., New York 
NY, J 970. $7.95 hardcover, 
$5.95 paperback. 

Anyone who wants to 
learn BASIC for the Altair 
system or any other BASIC 
system should have this book. 
The book has very clear 
explanations that make it 
easy to comprehend. 

The book is divided into 
37 two- to three-page lessons. 
There are four review tests 
and four test correcting 
programs. Yes, you program 



the computer to correct your 
test for you. The second half 
of the book contains 50 
review problems covering 
many different interests: 
algebra, geometry, finance, 
statistics, puzzles and games. 
At the end is a set of program 
solutions to problems in the 
book. 

The reader will start to 
write simple programs after 
the first three pages. After 
that, more of the language is 
introduced bit by bit with 
activity reinforcement of 
each new command. 

Lessons include: numbers 
and variables, order of 
calculations, built-in and user 
defined functions, flow 
charting, program looping, 
printing headings, inputs 
during execution, 
FOR-NEXT instructions, use 
of subroutines and matrices. 
All in all it is a very clear and 
comprehensive text for the 
learning of BASIC. 

Thomas Charles Greer 
224 N. Alabama St. 
San Gabriel CA 91775 




MICRO 440... the MORE 
affordable computer/ 




The MICRO 440, with a price intended to turn the competition's 
hair gray. It's built around the Intel 4040 CPU. And although it 
has only a 4-bit word, it's no toy. It features a powerful set of 60 
instructions to permit binary and decimal arithmetic, logic, 
loops and branching and real-time interrupts. It also features 
24 on-chip registers (more than many more expensive micros) 
and subroutine nesting to seven levels. With the bare-bones kit 
you get a single PC board housing CPU, clock, I/O interface, 
front panel controls and displays, and 256 bytes of 
program/data RAM. You also get our complete and instructive 
87-page manual. Order the complete kit, and you also get an 
enclosure, power supply, a standard input and output port and 
a standard Teletype interface. Need more memory? There's 
room for 8K of RAM or PROM memory, in 2K units. Each 
memory unit gives you extra I/O ports. 



The age of the microprocessor is here. They're already in 
sewing machines, parking garages, even pin-ball machines. 
Soon they'll be cooking your meals and controlling your TV. 
Have you been wanting to learn more about this exciting new 
technology? You could spend $300 to $600 to attend a course. 
Or, for less money, you can get unlimited hands-on experience 
with your own MICRO 440. With the basic kit you can enter a 
program up to 256 steps long, run and display the results. 
Following the simple instructions in our user's manual, you will 
learn the workings of the computer by loading and executing 
the many sample programs given, then learn to write your own 
programs. The usefulness of the MICRO 440 doesn't vanish as 
you learn. It's powerful enough to grow with you. Plug a 
Teletype or TV Typewriter into the back panel and greatly 
expand its capabilities. Add memory and peripherals, and 
you're ready for serious, efficient computing. 



Even fully expanded, the MICRO 440 won't cost you an arm and a leg. Would you believe a computer with 
2K PROM, 6K RAM, 32 1/0 ports, TTY interface, and a TV Typewriter for less than $1300? 




PRICES: Bare Bones Kit $175 

Complete Kit $275 

Assembled & Tested _ J 375 



PARTIAL KITS ALSO AVAILABLE. 
WRITE FOR PRICES. 




RO. BOX 1016 

HUNTSVILLE, ALABAMA 35807 

205-837-5100 




110 



LOGIC POWER SUPPLIES 

New Lambda transistorized, regulated, worth 2 or 3 times our price. 

1. (LVEE-5)OV,5 VDC74amp 125.00 

2. (LWD - 12) 12 VDC 26.5 amp 100.00 

3. (LMB - 5) 5 VDC 3.7 amp 40.00 

4. ( LMD - 1 5Y) 1 5 VDC 9 amp 45.00 







SOPHISTICATED LOGIC SUPPLIES 

By Dressen-Barnes and NJE. Transistorized, 
finely filtered and regulated. 1 15 volt input. 

#61-5S Output 5VDC 21 Amp 27 lb $47.50 

#51-5S Output 5VDC 10.5 Amp 16 1b 35.00 

#421-32 Output 32VDC3.3 Amp 12 1b 20.00 

#421-90 Output 90VDC1.2 Amp 12 1b 20.00 

#NJE 5VDC34 Amp 35 lb 75.00 




MEMORY SYSTEM $125.00 

New memory system by Honeywell, small . . . 
measures only 9x4x1 inches. 1024 core memory, 
1024 words with 8,9,10 bits/word. Random access, 
with all logic, register, timing, control, core select and 
sense functions in one package. New, booklet of 
schematics and data. Looks like a good beginning for 
a mini-computer. Limited supply on hand. 
Ship wgt 3 lbs. #SP-79 $125.00 



■■$S8B)& 
















1,000 mF 


15 volt 


$ .35 


2,000 fiF 


35 volt 


1.00 


2,000 


15 


.50 


19,500 


25 


$2.50 


1,000 


25 


.70 


12,000 


40 


2.50 


3,000 


25 


1.00 


3,900 


50 


2.00 


1,000 


35 


.80 


22,000 


75 


3.25 



COMPUTER 
CAPS 
BRAND 
NEW 



CORE MEMORY 

Another brand new memory, ultra small. Measures only 4x4 inches 
with format on one plane of 32 x 32 x 16 (16,384). Only about 35 
units of this on hand. 
#SP-81 $20.00 



SANDERS 720 KEYBOARD $40.00 



ytte&nMd 




FREE CATALOG 

Please add shipping cost on above. 

MESHNA P0 Bx 62 E. Lynn Mass. 01904 



111 



BOTE 



reader 
service 



To get further information on the products advertised in this 
issue of BYTE merely tear, rip, or snip out this advertiser index, 
fill out the data at the bottom of the page, mark the appropriate 
boxes, and send the works to BYTE, Peterborough NH 03458. 
Readers get extra Brownie Points for sending for information 
since this encourages advertisers to keep using BYTE — which in 
turn brings you a bigger BYTE. 

ADVERTISER INDEX 



□ American Cancer Society 91 

□ ACM 15 

D A. P. Products 2 

□ BYTE Subscriptions 95 

□ BYTE Retail Sales 110 

□ Bytronics 39 

□ Celdat 17 

□ Centi-Byte 18 

□ CMR 97 

□ Comp-Sultants 110 

□ Continental Specialties 81 

□ Delta Electronics 109 
D Dutronics 98 

a Godbout 6, 7 

□ Hickok 97,99 

□ lasis 56, 57 

□ IEEE 19 

D Int'l Elec. Unltd. 
D Intron 104 
D James 105,99 
D Martin Research 

□ Meshna 111 

□ Micro Digital 77 

□ Mikra D 104 
D MITS CIV, 40-47 

□ Ohio Scientific 102 
D Processor Tech. 28, 29 
D RGS 25 

D Scelbi 62, 63 , 

D Southwest Tech Clll 

□ Sphere 11, 13 

□ Suntronix 107 

□ Teleterminal 106 

□ Tri-Tek 101 
D Visulex 102 

□ Windjammer 92, 93 



103 



16 



Messages for the editor: 



Reader's Service 

BYTE 

Green Publishing Inc. 

Peterborough NH 03458 

Please print or type. 



Name 



DECEMBER 1975 

BYTE acquired via 

□ Subscription 

□ Newsstand 

□ Stolen 



Address 



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Zip 



Coupon expires in 60 days . . . 



THE 



BITE 



QUESTIONNAIRE 

BYTE is dedicated to the needs of its readership. 
In order to better gauge matters of editorial policy 
and content, as well as to give our advertisers some 
"hard facts," we publish this questionnaire. In this 
month's list are a few more questions of editorial 
interest: 

What applications do you have in mind for your 
own personal computer system? 



Do you presently have a computer? 



If you own or use a personal computer system, 
what is its CPU chip or main frame computer 
design? 



Have you had any "on the job" training using 
computers as a tool for some purpose? 



Do you know what a computer language is? Would 
you list the computer languages (if any) which you 
know? 



These questions are a short form "letter to the 
editor." If you have additional comments, don't 
hesitate to write! Send completed questionnaires 
to BYTE, Dept. Q, Peterborough NH 03458. 

Classified Ads Available for Individuals and Clubs 



Readers who have 
equipment to buy, sell or swap 
should send in a clearly typed or 
printed notice to that effect. 
Insertions should be limited to 
approximately 100 words or 
Jess. Advertisements for this 
feature can be accepted from 
individuals or bona-fide clubs of 



computer users only. 
Commercial advertisers should 
contact Bill Edwards, BYTE 
advertising manager, for the 
latest rate card and teims. 
Individual/club classifieds will 
be printed free on a space-avail- 
able basis in the earliest possible 
issue of BYTE. 



Feel free to photocopy this pane if you wish to keep your BYTE intact. 



112 



5Sifii6 




oo 



The Computer System You Hove Been Waiting For 
A BENCHMARK SYSTEM-Using the MOTOROLA M6800 benchmark microprocessor family. 






wlm* 





Southwest Technical Products is proud to introduce the M6800 computer system. This system is based upon the 
Motorola MC6800 microprocessor unit (MPU) and it's matching family of support devices. The 6800 system was chosen 
for our computer because this set of parts is currently in our opinion the "Benchmark Family" for microprocessor 
systems. It makes it possible for us to provide you with a computer system having outstanding versitility and ease of use. 

In addition to the outstanding hardware system, the Motorola 6800 has without question the most complete set of 
documentation yet made available for a microprocessor system. The 714 page Applications Manual for example con- 
tains material on programming techniques, system organization, input/output techniques, and more. Also available is the 
Programmers Manual which details the various types of software available for the system and provides instructions for 
the programming and use of the unique interface system that is part of the 6800 design. The M6800 system minimizes 
the number of required components and support parts, provides extremely simple interfacing to external devices and 
has outstanding documentation. 

Our kit combines the MC6800 processor with the MIKBUG® read-only memory (ROM). This ROM contains the pro- 
gram necessary to automatically place not only a loader, but also a mini-operating system into the computers memory. 
This makes the computer very convenient to use because it is ready for you to enter data from the terminal keyboard 
the minute power is turned "ON". Our kit also provides a serial control interface to connect a terminal to the system. 
This is not an extra cost option as in some inexpensive computers. The system is controlled from any ASCII coded 
terminal that you may wish to use. Our CT-1024 video terminal is a good choice. The control interface will also work 
with any 20 Ma. Teletype using ASCII code, such as the ASR-33, or KSR-33. The main memory in our basic kit con- 
sists of 2,048 words (BYTES) of static memory. This eliminates the need for refresh interrupts and allows the system to 
operate at full speed at all times. Our basic kit is supplied with processor system, which includes the MIKBUG ROM, a 
128 word static scratch pad RAM, and clock oscillator bit rate divider; main memory board with 2,048 words, a serial 
control interface, power supply, cabinet with cover and complete assembly and operation instructions which include 
test programs and the Motorola Programmers Manual. 



If you have a Motorola 6800 chip 
set, we will sell you boards, or any 
major part of this system as a separ- 
ate item. If you would like a full 
description and our price list, circle 
the reader service number or send 
the coupon today. Prices for a com- 
plete basic kit begin at only 
S450.00. 



MAIL THIS COUPON TODAY 

□ Enclosed is $450.00 □ or Master C. # 

□ or BAC # Ex Date 



Bank #_ 



For My SWTPC Computer Kit □ 



| | Send data package 



NAME 



ADDRESS 
CITY 



STATE ZIP 

Southwest Technical Products Corp., Box 32040, San Antonio, Texas 78284 



Tke MITS Altair 8800. 




(It's showing up in some or 

the most unusual places.)