Machine Code: e Game inventing e Lifein MC e Window

` Math: e Floating points e Linearregression :

Games and Programs:

e Lunar Landing Battleship Solitaire ZX80 Cipher Machine Tioga Toads Dice and Train

SYNTAX ZX80

A PUBLICATION OF

SYNTAX ZXS80 is a monthly newsletter exclusively for ZX80, ZX81 and MicroAce owners. We bring you news, reviews and applications for your computer, plus technical notes for circuit-builders. SYNTAX also provides a forum for thousands of users to share advice and problems about programs and vendors. We bring you timely updates about new hardware, software and books. And we cover all the Sinclair-MicroAce computers, including the new ZX81.

At SYNTAX we emphasize practicality. You can apply our suggestions even if you aren't sure at first why they work, because we give you complete instruc- tions. Text is clear and easy to understand. SYNTAX readers already know about:

e An automatic phone-dialer they can put to- gether in a few hours

e Syntactic Sums™ to check input for errors

e Printing characters four times normal size

* Programs to explore computer memory

e Cassette eavesdropping to locate files on tape and simplify loading

e How to build their own external additional RAM

e How to add an 8212 I/O chip to control external devices from their computers

And SYNTAX readers like what they get every month. Subscribers know they can depend on us.

After receiving only three issues of SYNTAX ZX80, I find that I anxiously await the next issue . . . keep up the good work!

Martin Irons

Goshen, NY Congratulations on the brass-tacks, down- to-earth approach of your newsletter. I'll be looking forward to future issues.

Otis Imboden

Washington, DC

Many readers get their first issue and immediately order the back issues — more proof that they like what they see.

YES! Please send me 12 issues of SYNTAX for $29.

L] My check for $29 is enclosed. Make checks payable to: SYNTAX ZX80, INC.

account number

THE HARVARD GROUP

What's special about our publication? Just look through one issue. We work hard to bring you a quality newsletter. We strive to print useful programs of above-average accuracy. As any computer magazine editor can tell you, program listing accuracy is tough to achieve, but we boost our average with every issue. We test each program to make sure it works, it fits in the designated RAM, and it runs when you follow the directions. We print program listings in screen-image format to make it easier for you (it's sure not easier for us!) to enter programs accurately. We invented Syntactic Sum!" as an additional aid for you in getting error-free programs. With your subscription you also get access to thousands of other readers, and our staff experts are available by phone to answer your questions or help you solve problems with your machine.

SYNTAX readers get every month: e Latest news of Z80 hardware and software * Programs to organize information, calculate, entertain, or instruct e Do-it-yourself additions to the ZX80/Micro- Ace/ZX81 e Clear explanations for beginners

To share the benefits of SYNTAX ZXS80, just com- plete the coupon below and return it with your choice of payment. You will receive a year's subscription, 12 issues, for only $29 in US funds (plus $14 for foreign airmail if you live outside North America).

We are so sure you'll find SYNTAX useful that we promise to refund your entire subscription fee if you aren't satisfied. An unconditional guarantee — you can't lose. But if you're still skeptical, send $1 for a sample issue and see for yourself how SYNTAX can help you use and enjoy your ZX80 or ZX81 more.

Join the others who stretch their ZX80s and ZX81s to the utmost. Act now — as soon as we receive your coupon with payment, your first issue will be on its way. For faster service, phone your credit card order to 617/456-3661. Don't miss SYNTAX!

Please charge my lJ MasterCard‏ لأ VISA [ ] American Express‏ لا Diner's Club account.‏ لأ

RD 2 BOX 457 HARVARD, MA 01451 exp. date bank number (MC only) l signature I own a لأ‎ Sinclair 0 EM Name Title [ ] Sinclair ZX81 Organization لأ‎ MicroAce computer. Address City State Zip Day Phone ( ) Evening Phone ( )

$182

The Sinclair ZX-81 is innovative and powerful. Now there's a magazine to help you get the most out of it.

Thousands of smart consumers have picked the Sinclair ZX-81 as their personal computer. And, unlike many of today's bar- gains, this one can really give you your money's worth. Or it can turn into nothing but an expensive calculator. A Sinclair owner can putter along in first gear, missing the power and potential of the ZX-81, or he can shift into high, pushing the ZX-81 beyond imaginable limits. That's why thousands of smart con- sumers have picked SYNC as their computer magazine.

Right on Target

The ZX-81 isunique. There is nothing like it, nothing that comes close to packing so much power and versatility into one small package. Some computer magazines might publish one or two articles about the Sinclair each year, some never mention it. SYNC covers only the ZX-81 and its predecessor, the ZX-80. If an article doesn't apply to the Sinclair, if a game doesn't work on the Sinclair, you won't see it in SYNC. Our staff and contributors are Sinclair owners. Some started out as experts. Others started as readers and became experts.

How can a whole magazine find enough material about one small computer? By cover- ing everything from hardware to software, by offering both new applications and old tricks with a new twist. Did you know that the Sin- clair can generate music? Our readers found that out when we published a program and article showing how to do it, and explaining why it works. Do you know where to buy soft- ware, books, or peripherals for the ZX-81? We list resources in every issue, along with ad- dresses for user's groups so you can get in touch with other Sinclair owners. But knowing where to buy is not enough by along shot. And that's where we can really help you out.

Hard-Hitting Evaluations

As a Sinclair owner, you know the value of a dollar. But it isn't always easy to know the value of all the extras on the market. Face it, some programs are great, some aren't worth the tape they're stored on. We receive every new product for the Sinclair as soon as it is available, often months before it is on the market. And those products are reviewed and tested with a very critical eye. If an adver-

GET IN oY NG

tiser doesn't care for this sort of honesty, we don't care for his business. We haven't gotten where we are by patting backs, we've gotten there by giving the Sinclair owner the informa- tion he needs. But there’s more to SYNC than just reviews.

Applications and Explanations

The ZX-81 comes with a very powerful Basic language. But power doesn't imply diffi- culty. We show you how to get the most from your computer, whether you want to write a game or keep track of a mailing list. And we don't stop with Basic. The Sinclair can be programmed in machine language. For the newcomer, we have articles explaining ma- chine language from the ground up. For the old pro (and anyone who has been reading SYNC for a while will soon find himself in this category) we have sophisticated routines for animation, data handling, and every other aspect of programming.

Don't run your computer in first gear.

Topping if off, hardware articles Cover every- thing from attaching a full-size keyboard to adding a tape monitor. Whether you are inter- ested in software or soldering, we'll keep you busy. But we also know how to have fun.

Games of Every Kind

If you like to shoot down attacking space- ships, fight monsters in a dungeon, or land on the moon, we've got what you want. Every issue of SYNC is packed with games. There are classic computer games converted for the Sinclair, and new games designed specifically to exploit the capabilities of the ZX-81. Our contributors keep getting better and better, but that's not surprising, because the games come complete with tips and explanations. Programming tricks and special techniques are fully explained, so you can use them in your own games. We don't believe in keeping secrets.

SYNC is a Creative Computing publication. Creative Computing is the number 1 maga- zine of software and applications with over 150,000 circulation. The two most popular computer games books in the world, Basic Computer Games and More Basic Computer Games (combined sales over 500,000) are published by Creative Computing. Creative Computing Software manufactures over 150 software packages for six different personal computers.

| Order SYNC Today | and Save Money!

| “الاك

$5 a year (cash payment in U.S. currency only) for all other countries outside U.S. and posses- sions. Please allow 60 to 90 days for delivery of

E spay |

SUPER INVASION

"The best Sinclair game to hit the market” — SYNC Magazine. A moving graphics game with three levels of play. SUPER INVASION challenges your Skill as you fire lasers at the attacking space invaders while maneuvering your Space craft to

avoid their deadly lasers. 1K $14.95

ZXCHESS

This sophisticated chess game has seven levels of play and a detailed display of the board. You can change sides and even change levels of dif- ficulty during a game. You can also start playing from any point in the game and if you get stuck, the computer will recommend a move. $24.95

16K

As commander of Starship Enterprise, you find yourself defending a galaxy overrun with the dreaded DRAKONS. Can you destroy them? With five levels of play and excellent graphics, you'll find SPACE TREK entertaining and challenging. Can only be used with the ZX81.

$14.95

16K

نا .2

REVERSI

if you like Othello, you'll love REVERSI. With the board displayed, you can go first or let the computer go and you have a choice of starting

positions. 1K $14.95

MACHINE LANGUAGE PROGRAMMING

Made Simple For the Sinclair ZX81. This book is a complete guide in machine

language for the beginner. BOOK $19.95 UNDERSTANDING YOUR ZX81 ROM

This book gives an overview of machine language and describes the operation of the Sinclair ROM. Essential for the serious programmer.

COMING SOON: PACKPERSON

AND MANY MORE ZX81 PROGRAMS! FOR FREE CATALOG.

(Programs can also be used with the 1 K

WALLBUSTERS

"A breakthrough in creating active display games.'-SYNC Magazine. WALLBUSTERS | challenges you to break through two barricades | using nine balls and a curved bat. With seven ١ levels of play, WALLBUSTERS is hard to beat. ds You'll be amazed at the superb graphics in this 1K

game. 1K $14.95 ADVENTURE “A”

Your space ship is marooned on a strange planet but you can get out if you make the right combina- tion of decisions. Written in machine language, this challenging adventure has over 100 words of

vocabulary. 16K $19.95

ADVENTURE “B” À

; 2^ ١ k

Enter the long lost Inca Temple, find your way A through the tricky tunnels and corridors and you may find the lost treasure. Or you may be lost forever.

SN

16K $19.95

ROAD TO RICHES

What would you do if someone gave you a million dollars to invest? Would you make more money or lose it all? This investment game combines luck and strategy to challenge up to four players to heel and deal their way to riches...or ruin.

16K $14.95 TEN EXCITING PROGRAMS FOR THE ZX81: 1K

These BASIC programs on cassette include Lunar Lander, Space War and Brands Hatch. In- cluded are complete listings and suggestions so you can learn and adapt programs. Can only be

used with the ZX81. 1K $14.95 DIRECTORY/RECORD

Two programs on one cassette with full listings. The DIRECTORY program allows you to read names of programs saved on cassette. The RECORD program allows you to save and load 96 Byte data records on tape and can be incor- porated into other programs.

$14.95

WRITE

ZX80 with 8K ROM unless specified.)

BOOK $19.95

ALL PROGRAMS ON CASSETTE PRICE QTY | AMOUNT SUPER INVASION 14.95

WALLBUSTERS 14.95

ZXCHESS 24.95

ADVENTURE “A” 19.95

ADVENTURE "B" 19.95

SPACE TREK 14.95

REVERSI 14.95

ROAD TO RICHES 14.95

TEN EXCITING PROGRAMS 14.95 DIRECTORY/RECORD 14.95

MACHINE LANGUAGE 19.95

UNDERSTANDING YOUR ROM 19.95

SHIPPING AND HANDLING 1.50 $1.50

SALES TAX (NY RESIDENTS ONLY)

TOTAL:

SEND CHECK OR MONEY ORDER TO:

SOFTSYNCG, INC.

PO Box 480, Murray Hill Station, New York, N.Y 10156

New York residents add sales tax.

NAME

ADDRESS

CITY

STATE/ZIP

The magazine for Sinclair users

Ei irr

January/February 1982 Volume 2, Number 1 DEPARTMENTS REVIEWS 4 LOL ......... ع‎ Gow ESO RR EEROJARNREERq MES 26 You May Fire When Ready, Gridley!.......... Sampson Software Review 8 SYNC Notes........................... sese Grosjean 21 MicroAce Video Upgrade...................... Keeney 10 Perceptions. .........Lusuuu uuu esses Orstein Hardware Review 4K and 8K ROM command conversions MATH AND HARDWARE 12 Kitchen SYNC...... In Groupe, Tardiff, Zatkovich 30 Understanding Floating —Point Arithmetic....... Logan To build or not to build? ZX81 Kit review Part 1— Decimal and binary formats 1 5 Writing for SYNC............................ Grosjean 32 Linear Regression............................. Passler Relating two variabl 1 5 Try This......................... n RB Grosjean 59 MES 19 Puzzles and Problems....................... rownsend | 8 اا ا ی ا ت ی ی‎ schaal 25 Glitchoidz Report. .............................. sss GAMES AND PROGRAMS 44 A P يع ع العم وم قمع ملعا ممم مم ممعم مع‎ ns 33 Lunar Lander.......................... Dawson Try your piloting skills MACHINE CODE

Publisher/Editor-in-Chief Managing Editor Associate Editor Secretary

Production Manager

Art Director

Assistant Art Director Typesetters

Financial Coordinator Personnel and Finance Customer Service Circulation

How to Invent a Game. ...... .........Bobst

Basic and machine code techniques

The Game of Life Revisited — An Assembly Version ........................... Booth Generation in MC

WindOoW......................... sss Ornstein Machine language monitor

Staff

David H. Ahl

Paul Grosjean David Lubar Elizabeth Magin Laura MacKenzie Susan Gendzwil Diana Negri

Jean Ann Vokoun Maureen Welsh William L. Baumann Patricia Kennelly Ralph Loveys Frances Miskovich Carol Vita

Artic Computing

Books for the ZX81 Burnett Electronics Byte Back

Computer Coin Games Gladstone Electronics Harvard Group

JMC

JS&A

Kopak Creations, Inc. L.J.H. Enterprises Marex

Melbourne House Mindware

Professional Electronics

RKL Systems Sinclair Research Softsync, Inc. SYNC subscriptions

January/February 1982

Be a Computer Literate

Katie and the Computer

Index to Advertisers

Colossal Computer Cartoon Book

Battleship Solitaire. ....................... Dusenberry Sink the hiding ships

The ZX80 As a Cipher Machine. ......... Hollandsworth Machine coding and decoding

Tioga Toads............................. Bobst Dice and Train................................. Sutton

Two 1K games

Volume 2, Number 1

9 ‘SYNC (USPS: 585-490; ISSN: 0279-5701) is published 29 bi-monthly for $16 per year by Creative Computing,

cover 4 39 E. Hanover Ave.. Morris Plains, NJ 07950. 11 Second class postage paid at New York, NY 10016, 13 and at additional mailing offices. 39

39 Subscription rates: USA: 6 issues $16; 12 issues

7 $30; 18 issues $42. Canada: $3 per year additional. Other foreign: $5 per year additional. U.K. Air: 6 27 issues £13. Minimum charge card order $10.00.

29 U.K. address: SYNC, 27 Andrew Close, Stoke 9 Golding, Nuneaton CV13 6EL.

31 Postmaster: Send address changed to SYNC, P.O. Box 789-M, Morristown, NJ 07960.

creative competing

PUBLICATION

8K ROM Double Image

Dear Editor:

To answer partially Joe Sutton's question (SYNC 1:4) about the 8K ROM’s “double image,” I noticed the same thing with the 4K ROM: 4 “images” of the same 4K monitor program were to be found in the 16K addressing space set aside for system ROM. I reasoned that the unneeded most significant bits of the address bus were ignored, enabling the ROM chip whenever the address was below 16K. Thus, for the 8K ROM, address 0 and address 0 plus 8K are interpreted as the same address. The 8K bit is ignored. However, I do not understand the nitty-gritty hardware aspects fully (the ROM appears to have both the A8 and A12 address lines connected to chip select).

I would like to see an indepth discussion of the ZX80's discrete components (not much to discuss in the ZX81!). I would also like to see more articles on the 4K and 8K ROMs as well as hardware inter- faces. For instance, I would like to purchase a surplus terminal (Model 15 or Model 33), but I do not know whether the standard Z80 interface will suffice or what modifi- cations of the 8K ROM's LPRINT are needed.

As a math teacher I would like to see articles on educational applications since with tight money in government the inex- pensive, but effective ZX81 may be the only realistic choice for today's schools.

Ireally have to compliment Mr. Sinclair on the improvements and reduced price of the ZX81. I only wish I would have purchased a ZX81 kit rather than an 8K ROM upgrade; then I would have two computers and smooth display for only $60 more. It would also be nice to have more on board RAM. So how about an article on constructing a memory upgrade using one of the many available RAM PC boards?

4

I would also like to see an article on constructing or interfacing a 2716/2732 EPROM programmer (student proof pro- grams!

Timothy MclIlwee Granada Royale Rm. 121 Route 1, and I-95 Ormond Beach, FL 32074

Ed. — Here is a list of challenges for SYNC authors. Similar requests have come from other readers.

Taxman

Dear Editor:

The program Taxman that appears in SYNC (1:6) is an interesting mathematical game. The listing (as printed) does contain one minor bug. Line 630 should read

630 FOR 1-3 TON

to cover all possible cases. It would not hurt if, in fact, that line were to read

630 FOR I=1 TON As presently written, line 630 will not allow the computer to have credit for a remaining unused value of 3. To test this out, run the program for a set of 5 numbers.

It is not difficult to show that for a set of 30 numbers, the best score attainable is 301 to 164. The opening choices are 29, 25, 15, and 27. The remainder of the solution is left as an exercise for the reader. The first move in this game is obviously to pick the largest prime number in the set.

Peter D. Hoffman 5618 Martinique Dr. Corpus Christi, TX 78411

An Inventory System

Dear Editor:

In reference to Dr. Stephen A. Justham’s article entitled “An Inventory System,” much space and some computing time can be saved in the search sequence by making the following changes:

3 DIM R$(1,15) 3040 INPUT R$(1) 3042 delete 3044 delete 3052 delete 3068 IF R$(1)—IS(B) THEN GOTO 3100 3115 PRINT TAB 5; R$(1)

By setting up a single position array of 15 length at line 3, the input at line 3040 is automatically adjusted to equal the elements of the I$ array. This saves setting up the 151 position M$ array, resulting in a saving of up to 2,250 bytes of RAM.

Ralph Goodrick 3700 W. 151st Stanley, KS 66224

Hampson's Plane

Dear Editor:

I feel "Hampson's Plane" is one of the better 4K/1K games you have published. I made a minor change to make continuous play easier. Add lines: 1CLS 105 IF K$—"X" THEN GOTO 1

When one has completed a plane (or whenever an alpha coordinate is requested) an "X" can be entered to return to the beginning of the game. I also suggest that the string in line 20 be changed to one space. It makes the appearance of a plane similar to the one published in the article.

Robert Masters 396 Billerica Road Tewksbury, MA 01876

SYNC Magazine

Remembering numbers is genie work.

A fairy tale? The story you are about to read may be true or it may be false.

If the story is false, we've wasted a lot of your time. If the story is true, well...you might just make a lucky discovery. Here's why.

Your push button telephone has a bunch of buttons that make beeping sounds when you press them. The beeping sounds send signals or actually ‘talk’ to your phone company and its computerized switching system. Thats how calls are made.

Now think of it. What if your phone was first connected to your own telephone computer. And what if in your own telephone computer you had a real genie that actually took your command and performed electronic magic on your phone lines. Far fetched? Read on.

WHAT KIND OF MAGIC

What if the system proved to be the fastest and most positive way to reach another person at another phone regardless of whether the phone is busy or whether that person is even near a phone. Enter Busy Buttons.

Busy Buttons is a miniature computer in a small black box. The box is nothing much to look at, measures only 112" x 5" x 534" and in fact most people would probably hide it. The box plugs into the back of any telephone in your house or any multi-line telephone in your office. That's right, just plug it in. No installa- tion, no wires to connect. Just plug it in.

HERE IT COMES

Now here comes the fairytale part. In that black box is indeed a real genie-a small creature so smart that it will understand every command you give it from your telephone's push buttons. No foolin'.

If you dial a number and that number is busy, you tell the genie you're upset by pressing the ‘frustration’ button—that’s the button with a star on it. The genie will first redial that same number ten consecutive times the first minute and then once every two minutes thereafter until it reaches your party. When the call does go through, your genie will then signal you to

pick up the phone. And you can still make calls and receive calls in between those times your genie is trying to reach the other party.

But what if there's no answer? After you let your phone ring for awhile, press the 'disap- pointment' button. The genie will then dial your number every ten minutes for up to ten hours and then signal you when somebody answers.

GENIES NEVER FORGET

"But what if the genie forgets the number it was dialing?" you might ask. The answer is quite logical. Genies never forget. In fact, you can own a genie so smart it will remember up to 176 numbers each up to 32 digits so you can not only dial long distance, you can use your genie to dial the entire 23 digit MCI or Sprint numbers in seconds. Your genie will recognize the tones, the pauses and faithfully dial your number accurately each time saving you tons of money on long distance charges.

“Too complicated," you might say. For your genie it might be but not for you. Remember, you use your own push button phone. There's no other attachment other than that dumb black box where your genie lives. And when you want to dial a number, you dial PAUL to reach Paul, MOM to reach your mom or HAIR to call your hair stylist. Remembering names is easy, remembering numbers is genie work.

THE REAL SHOCK

Ready for a real shock? You only need one genie to cover every telephone in your house or office. That's right. Unlike other auto dialers, one genie is all you need to turn every phone into this fully automatic system. But wait, there's more.

Genies talk differently. The American genie talks very rapidly in tones like most push button phones. There is even a Japanese genie that talks slowly and methodically in a pulsating sound similar to a rotary dial tele- phone. This means you can use Busy Buttons on push button or rotary dial telephones.

The Busy Button system is quite inexpen- sive. Genies you see have no minimum wage,

Bu Buttons

Turn those innocent little buttons on your telephone into Busy Buttons and release the genie from its little black box.

ELECTRONIC FAIRY TALE

SY

are exempt from EEOC, EPA, OSHA, FDA and HEW regulations and don't mind putting in overtime or washing windows.

DIFFERENT VERSIONS

A 176 number Busy Buttons costs only $200 —the 93 number version costs $180. If you want the Japanese Genie, you can have either model for $20 cheaper. And you can order Busy Buttons using your credit card by calling our toll-free number below. (Illinois residents add 696 sales tax.) Or send your check for the amounts listed above plus $4.00 for postage and handling to the address below.

When you receive your Busy Buttons com- puter just plug it in. That's right, plug it in. Then see how easy it is to program, how easy it is to redial a number either yourself or automat- ically. If you're not happy with the convenience of the Busy Buttons or the time and money you save from the day you install it, return it any- time within 30 days for a prompt and courteous refund including your $4.00 postage and handling charge. It won't cost you a penny and you won't insult the genie.

At the beginning of this advertisement we told you that the above story may be true or it may be false. Well it’s true. There really is a genie in every Busy Buttons. And if you believe that, wait till you hear about our new compu- terized burglar alarm with its own built-in SWAT team. Order your Busy Buttons at no obligation, today.

9) M PRODUCTS S ١ eA THINK

Dept. SN One JS&A Plaza Northbrook, Ill. 60062 (312) 564-7000 Call TOLL-FREE ........ 800 228-5000 In Nebraska Call ........ 800 323-6400

(OJS&A Group, Inc.,1981

Flag Use Tip

Dear Editor:

I wish to pass on a tip to readers of SYNC concerning flags. In games involving two players (and in other two-way situa- tions), flags are often used to determine which group of data is to be used. The actual setting and resetting of flags would usually go something like this:

10 LET A=0 100 LET A=1 (or 100 LET A=A +1).

Suppose that you don't know if the flag 15 set, but you want to change its state. You have to type:

100 IF A=1 THEN GOTO 115

105 LET A=1

110 GOTO 120

115 LET A=0

A much easier way is to type

100 LET A=ABS(A-1).

This does the exact same thing with much less memory space.

Philip Gervais 714 5th Ave. So. Clinton, IA 52732

MINDWARE CO.

ZX80/81 World

Dear Editor:

Wow! Am I ever impressed. I had no idea of the breadth of the ZX 80/81 world. As I have had my ZX 80 only two months, some things in the programming completely eluded me. My very first issue of SYNC (1:5) really opened up a lot of grey areas for me.

Anyhow, the main reason for this letter is the availability of the first 4 issues. If you have them on hand, please mail and bill. If not, do you know of an outlet for same.

I will appreciate any assistance.

Tony Wall

Ed. — At this point we have only a few copies of 1:2 and 1:4. Back issue orders must include payment of $2.50 per maga- zine. There are no other outlets.

The Great Circle Route

Dear Editor:

I enjoyed Chuck Dawson's "The Great Circle Route" (SYNC 1:5) and found it a good exercise to use it in conjunction with a standard mileage chart which gives distances in nautical miles. However, I felt that the addition of city names and approx- imate cost would make an interesting improvement. The cost figures are based on the average cost of Transcontinental U.S. flights and can be changed by adjusting the .009 figure in line 205.

A report code 5 (FULL SCREEN) will appear after destination LATITUDE prompt and it will be necessary to use CONTINUE.

The program changes are:

20 PRINT "ENTER DEPARTURE CITY"

21 INPUT A$

23 PRINT A$

100 PRINT “DESTINATION CITY”

101 INPUT B$

103 PRINT B$

185 PRINT A$;,ZB$

205 PRINT “COST#$”;.09*DIST ;“####”

H.S. Wake 4171 Stettler Way San Diego, CA 92122 Fa

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Our address is: MINDWARE CO. 70 Boston Post Road, Wayland, MA 01778 (617) 358-7175

9 SYNC Magazine

Make the most of your Sinclair Computer . . .

Software on Cassette!

MULTIFILE Data Storage System An amazingly versatile multi-purpose filing system for the 16K ZX81. The program is menu- driven, and number, size and headings of files are user-definable. Both string and numerical files are catered for. Files may be created, modified, replaced, and searched, and are protected by an ingenious foolproof security system. Output to the ZX printer is also provided.

The program comes on cassette, together with three quality data cassettes for file storage, and com- prehensive documentation, describ- ing a host of applications for both business and personal use. If your ZX81 is bored with playing games, then this program will give it plenty to think about! . .$29.95 ($39.95 in Canada)

ZXAS MACHINE CODE ASSEMBLER Bored with BASIC? POKEING not your scene? Learn and program in machine code the easy way with this powrful Z80 assembler, commissioned specially for the ZX81 & ZX80.

Standard Z80 nemonics are simply written into REM statements within your BASIC program. The assembly listings, together with addresses and assembled codes are displayed on the screen when assembled. The assembled code is executed with the USR function. The program uses 5K of memory and is protected from overwriting. Full documentation, in- cluding examples, is supplied with the cassette. This program is a must for all serious ZX81 & ZX80 users. ...

$9.95 ($12.95 in Canada)

Last Minute Addition: ZXDB

The perfect complement to ZXAS assembler, ZXDB is a complete combined machine code disassembler and debugging program. May be used in conjunction with ZXAS and will leave about 9K of memory for your own program. Additional features in- clude Single Step, Block, Search, Transfer and Fill, Hex Loader, Register Display and more. Executed by single keyboard entry. The combination of ZXAS/ZXDB plus one of our books will teach you all you need to know to program in machine codes.

ZXDB .. $9.95 ($12.95 in Canada)

[L1 1 1l loeo eoe oe ee o e e e d

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MACHINE LANGUAGE MADE SIMPLE FOR ZX80 and ZX81. A complete beginners quide to machine language programming. Go beyond BASIC and open new computer horizons! Finally find out what PEEK and POKE is all about. Machine language program enables more com- puting power in less space, faster running programs. The 120 pages of this book are packed with programm- ing techniques, hints and tips; useful BASIC program to edit machine language; numerous sample routines;

easy-to-use reference tables. $19.95 ($23.95 in Canada)

UNDERSTANDING YOUR SINCLAIR ROM. A more advanc- ed publication explaining the various ROM features.$19.95 ($23.95 in Canada)

ZX CHESS!

(for ZX81 and 8K/ZX80 both with 16K RAM)

A challenging chess programme, written in machine language, designed to operate in the ZX81 fast mode. ZX Chess allows you to select from 6 levels of play, choose either black or white, and enables castling and en passant moves. Unique “self-running” feature: you start the tape and when the chess board appears on the screen, start your game

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The ZX81 Pocket Book

Written in the informative and clear style of the earlier, highly successful ZX80 Pocket Book, but with all new content. This is the ideal follow-up to the Sinclair manual, with application to both ZX81 and 8K ROM ZX80! The ZX81 Pocket Book begins with an exceptional 1K RAM programme (Pinning the Tail on the Donkey), which is followed by revealing chapters on String-Functions and Efficient Programming. Throughout there is a balance between serious computing concepts and fun programs. A particular emphasis is placed on the use of subroutines. Ohter chapters provide Hints 'n' Tips, Decimal Justification, Using Machine Code, Numeric Conversion, and ZX81 Adventure. Programs for both 1K and 16K machines include: Ski Run, Ball & Bucket, Etch-a-Sketch, Digital Clock, Standard Deviation, Dice Simulation, City of Alzan (a long adventure program), plus many others. The book contains 5 appendices containing ZX80 and ZX81 con- versions, ZX81 module selector listing, solutions to prob- lems in the book, ZX81 Basic command summary, and error code summary. The emphasis throughout is on a programming style designed to conserve memory, and demonstrate practical techniques to make your programs function better. Every Sinclair owner should have a copy right alongside his manual!

The ZX81 Pocket Book. by Trevor Toms, Phipps Associates. 136 pages. Spiral bound. $11.95($14.95 in Canada)

NOT ONLY 30 PROGRAMS FOR THE SINCLAIR ZX81 BUT ALSO... detailed explanations and much much more. All programs designed to fit into the 1K memory of the ZX81. Includes such favorites as Star Wars, Lunar Lander, Blackjack, Mini Adventure. Also explanations of how programs were written, hints on how to write your own exciting pro- grams, space-saving techniques, peeks and pokes and other “com-

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MicroAce Discontinues U.S. Operations

MicroAce has discontinued its U.S. operations as of mid-December 1981, but arrangements have been made for repair services on MicroAce equipment. Micro- Ace owners with problems should con- tact:

Bob Ward 3176 Oak Knoll Los Alamitos, CA 90720

Problems and complaints may be also

directed to MicroAce's U.K. address: MicroAce Compshop 14 Station Road New Barnet Hertsfordshire EN5 1QW United Kingdom

MicroAce is also looking for distributors who will represent MicroAce in the U.S. for continued sales of the video upgrade board. lf you are interested, write MicroAce at the U.K. address above.

Sinclair to Replace Defective MicroAce 8K ROMs

Sinclair has announced that defective MicroAce 8K ROMS will be replaced by Sinclair if the ROM is sent along with $10 to:

Sinclair Research Ltd. 50 Staniford St. Boston, MA 02114

Sinclair Policy Change on Technical Phone Inquiries

Sinclair has discontinued the policy of dealing with technical questions on the Sinclair computers by phone. Among the reasons cited for this change are: 1) the volume of sales; 2) the increasing proportion of kit sales which raise more complex

8

questions difficult to answer by phone; 3) many inquiries have to do with applications rather than the actual computer opera- tion.

However, the repair policy remains unchanged. lf you are having problems with your computer, it can be returned to Sinclair for either repair or replacement free of charge within 90 days of purchase.

An attempt will be made to answer technical questions for owners of the Sinclair computers addressed to: Sinclair Research Ltd., 4 Sinclair Plaza, Nashua, NH 03061.

SYNC NOTES U.K. Win a £1,000

[Ed. — We received the following announce- ment from Prestel:]

British Telecom's Prestel —the world viewdata servie —is offering a prize of £1,000 to the designer of the best Prestel adaptor for the Sinclair 1

Telesoftware — computer programs dis- tributed from a central source via teletext or viewdata to computers in schools, homes and offices—is a growth area on Prestel. Following the initiative of the Department of Industry in funding the Council for Educational Technology's Educational Telesoftware Project, many program pub- lishers are becoming active with program libraries of up to 1,000 pages strong being established.

Since the Sinclair ZX81 is yet without Prestel adaptation, Prestel is offering a prize of £1,000 which will be awarded to the designer of the ZX81 adaptor which combines best the elements of low price, elegant design and practical robustness.

The closing date for the competition is March 14, 1982. A working prototype capable of being modified so as to receive approval for attachment to the telephone network must be submitted. Designs will remain the property of the designer.

Further details, specification, and entry forms are obtainable from Tony Sweet, Prestel Headquarters, Telephone House, Temple Avenue, London EC4Y OHL. Telephone 01-583 9811.

The object the ZX81 competition is to design a system which will be capable of loading ZX81 software contained on a Prestel frame into the RAM of the machine and be ready to run.

Rules:

a) The adaptor must work to Prestal frames in CET format.

b) It must be capable of production on a commercial basis, i.e., using readily available components.

c) It should be “in the spirit of the ZX81,” i.e., low price, practical robustness, and efficient design.

d) It must be capable of modification to receive approval for the attachment to the telephone network.

e) A detailed circuit diagram/parts must be submitted with the completed entry. This will be treated in strictest confidence by BT.

f) Designs and prototypes will remain the property of the designer.

g) The judges decision will be final. No correspondence will be entered into over the | acceptance/non-acceptance of entries.

h) Entries must be received by 14 March 1982 and must be demonstrated by the designer before acceptance. Arrangements will be made for designers to have editing access to Prestel as necessary.

i) Completed entry forms must be sub- mitted to BT before designs are sub- mitted.

SYNC Program Listings

Readers should note the following con- ventions used in the program listings in this issue:

# ore = Used in PRINT statements to show necessary spaces.

“A” (shift) = Used in PRINT statements to indicate graphics; in this case use the graphic on shift A.

INPUT = Used in PRINT statements to show that the keyboard key or token should be used instead of spelling out the word.

SYNC Magazine

Sinclair 8K ROM Problems?

In SYNC Notes (SYNC 1:5) we gave a test to check whether you had received a defective ROM. The following letter from Nigel Searle will clarify this matter further:

sj

1K GAMES PACK £3.00

Dear Customer:

The recent mention in Sync magazine of a possible bug in our 8K BASIC ROM could be misleading.

The correct value of 23 is 4,294,967,296. This is rounded to 8 sianificant

digits and displayed as 4,294,967,300. 2°°7! is 4,294,967,295 which, when rounded to 8 significant digits, is also displayed as 4,294,967,300.

This is the appropriate result for a computer of finite (8 digit) capacity.

The bug referred to in Sync will give 1,288,490,200 when 1 is subtracted

Y fron 232 (4,294,967,300). Only if your ROM has this problem should you JÉ A return it to us for replacement. ET f, Singere Nigel H. Searle a" "Now there's a real hex sign!"

MOVING AHEAD WITH ZX SOFTWARE

16K RAM PACKS ZX CHESS ONLY £35.00 & ADVENTURES

PROGRAMS FOR THE ZX81/80 INCLUDING —

ZX CHESS I ADVENTURE ‘A’, . £5.00 an alien planet. Ted Uem 10: £8.00 Can you reach your ship and ZX CHESS II escape?

now only: £14.00 ADVENTURE ‘B'

ADVENTURES £7.00

Very popular machine code program, with six levels of play and an analysis option. Unbeaten except by: 55 A new improved version, with ADVENTURE C, a faster response time, seven £7.00 levels of play, and in addition a Can you reach the control room recommended move option. and free yourself or will they get Exciting machine code games you first? with instant response, choose Includes a cassette save from the range below. routine.

You find yourself stranded on

In a jungle clearing you come acrossan Inca temple. You must break in, collect treasure and escape alive. Beware. Includes a cassette save routine.

You are unfortunate enough to be drawn to an alien cruiser.

GALAXY WARRIOR £3.00

and many more. Foracatalogue giving full details, please send a S.A.E. to,

Fast and exciting interactive animated graphics game. Hunt clingons and go through black holes...

ARTIC COMPUTING 396 JAMES RECKITT AVENUE HULL, HU8 OJA. U.K.

January/February 1982

KOPAK GIVES YOU THE POWER!

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The KOPAKTM Sinclair* female Con- nector gives you the power to use the 2-80 bus. Edgecard connectors specif- ically made for Sinclair* computers. e 46 Pins, 23/23 * All pins are gold plated e polarizing pin for correct alignment everytime! Available with Solder-Tail, Wire-Rap and PCBoard. $14.95

‘KOPAK has the POWER to deliver!’

Order by Phone or Mail, Charge it with MasterCharge or Visa

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KOPAKTM is now offering The Source* ‘America’s Information Utility’. The Source* gives you the power to access a wide array of services including: e Barter e Shopping * Business Infor- mation e Career Network e Electronic Mail e Medical Advice e UPI News Service and much more. A modem is required to use The Source™.

Source ID $100.

More POWER on the way! KOPAK’STM Coming Creations: The KOPAKTM RS-232 Interface The KOPAKTM Bus The KOPAMATICTM Keyboard The KOPAKTM Printer KOPAKTM Memory Products The KOPAKTM Disc

(O 1982 KOPAK Creations Inc.

TM Trademark of KOPAK Creations Inc.

Sinclair* is a trademark of Sinclair* Research LTD.

MicroAce* is a trademark of MicroAce*

4K ROM 8K ROM

Perceptions |

David B. Ornstein

4K and 8K ROM

Command Conversions

In the last issue of SYNC (1:6) I began a discussion of the conversion of programs from the 4K Integer Basic to the 8K F.P. (Floating Point) Basic and covered expres- sions and functions. In this issue I will conclude the discussion by detailing the processes necessary for the conversion of commands from one ROM to the other.

The following commands are 100% transferable from a program on one ROM to a program on the other ROM:

LET REM

NEW IP... THEN RUN INPUT CONT (INUE) PRINT STOP LIST GOTO POKE RAND (OMISE) CLEAR GOSUB RETURN

Because a parallel for each of the com- mands in the 4K ROM exists in the 8K ROM, I will list alphabetically all the 8K ROM commands. When possible, a 4K ROM conversion will be given. (The names of the 4K commands will be given in brackets.)

CLS [CLS]

The CLS command is used to clear the entire (TV) screen. On a 4K ROM system or an 8K ROM system with less than 3.25K of RAM, the CLS command works identi- cally (i.e., it creates a minimal display file). On an 8K machine with more than 3.25K

10

of RAM, a full display file, padded with spaces, is created. The command is gener- ally interchangeable between ROMs.

COPY

The COPY command is used to print the screen, as is, on the ZX Printer. As the printer cannot be used with a 4K ROM system, there is no simulation available to perform a parallel function.

DIM [DIM|

DIM is used to create arrays and matrices. On the 8K ROM, both numeric (F.P.) and string (character) arrays are available. On the 4K ROM, only numeric (Integral) arrays are available. As noted earlier, (see Percep- tions, SYNC 1:6), there is no way to use floating point numerics on a 4K system. String arrays are also, generally, out of the question.

The 4K ROM's integral arrays are useful in that they save 3-bytes per number. If you have an application that really needs integral arrays because of memory size constraints, a method can be derived to emulate them. As usual, the gain in space will result in a slow-down of the system.

Imagine a situation in which you want a 100-element intergral array. Running the 4K Basic, to allocate it, you might type:

DIM A(100) This would instruct the system to reserve 200 bytes for the elements of the array (2- bytes each). To reference the 40th element, you might use the statement: LET J = A(40)

My 8K emulation is relatively simple. In place of the original DIM statement, use the following:

DIM AS(200)

Then, to reference the 40th element, you would use an expression like:

LET J = CODE A$ (39*2+1)+ CODE A$(39*2+ 2)*256

This method accesses the appropriate element’s value by reading its 2 data bytes and combining them, putting the result into the variable J.

To change the value of an element, you might use the following sequence:

10 LET TEMP=INT(J/256)

20 LET A$(39*2+ 1 TO 39*2+2) = CHR$ (J- TEMP*256) - CHRS(TEMP) This would set the 40th element to the value of J and is equivalent to:

LET A(40)=J

Generally, the subexpression to use if you want to reference the Xth elementis:

CODE A$ ((X-1)*2+1)+ CODE AS((X- 1)*2-4-2)*256

FAST

FAST isa command used to control the video mode of the ZX81. The ZX80 (i.e., 4K ROM) is always in FAST mode.

FOR...NEXT (STEP) [FOR...NEXT |

The FOR and NEXT commands are used to set up a loop in the program. The 8K version has two features not imple- mented on the 4K version. The first is that you may have non-integral values for the looping variable. This cannot be simulated on the 4K ROM. The other feature, a STEP modifier, can be simulated.

If you run the following program:

10 FOR 1-1 TO 10

20 PRINT J

30 NEXT J you will see the numbers from 1 to 10,

SYNC Magazine

= —" ———————————————

Ei 1 = E E E E E : 3 EK د وك‎ REE EEUU O,

REN

as

stepping by 1, printed on the screen. If, on an 8K ROM, you run the program:

10 FOR J=1 TO 10 STEP 2

20 PRINT J

30 NEXT J you will see the numbers from 1 to 10, stepping by 2, printed on the screen.

The first program is equivalent to the following:

10 LET J=1

20 PRINT J

30 LET J=J+1

40 IF J<11 THEN GOTO 20

Notice that in line 30, the value stored in

J is incremented by one. To make this run as per the 8K program, add line 5 as follows:

5 LET ST=2 and change line 30 to say:

30 LET J=J+ST Now it will run and print the numbers from 1 to 10 on the screen, stepping by two.

LLIST

The LLIST command is used to list out the program on the ZX Printer. As is the case with the COPY command, it is not possible to use the printer, and, thus, the printer commands, on the 4K ROM.

LOAD [LOAD]

The LOAD command is used to bring a previously SAVEd program back into the computer. The 8K version uses a file name (possibly null) to specify which program on the tape you want to LOAD. The 4K version simply takes the next program on the tape and LOADS it. The formats on 4K and 8K programs involve such a differ- ential as to make it a fruitless venture to attempt to LOAD a program SAVEd on a 4K machine into an 8K machine, or vice versa.

LPRINT

The LPRINT, used to print a line out to the ZX Printer, has the same constraints applied to it as does LLIST.

PAUSE

The PAUSE command is used to delay for a given number of frames on the TV (16ms), while continuously scanning the picture. Barring a moderately complex machine language program, it cannot be simulated. (For those interested, I suggest my article “The ZX80 Keyboard” (S YNC 1:2), which describes the keyboard/display scanning routine, as a good starting point.)

PLOT/UNPLOT

These commands are used to PLOT particular graphics points on the screen. There is no completely parallel function on the 4K ROM. It must be done with a PRINT statement.

SAVE [SAVE]

The SAVE command, used to SAVE the current program on tape for later retrieval, is available on both ROMs. The only difference is that the 8K version takes a name as an argument.

SCROLL

SCROLL (SCreen ROLL) is used to roll the entire screen up one line. Although no parallel exists in the 4K Basic, it can be (and has been) simulated with machine language. See Ian Logan's article "Screen Scrolling" (SYNC 1:4) for more details.

SLOW

The SLOW command, like the FAST command, is used to select the video mode of the ZX81. It is non-functional on a ZX80 with an 8K ROM and cannot be simulated on a 4K machine.

16K RAM Pack Schematic Corrections

A number of readers have noted some problems with the 16K RAM pack schema- tic printed in SYNC 1:5. The following corrections should be made:

1) On IC 7 no pin 13 is listed, but it should be shown and connected to pin 6.

January/February 1982

2) On ICs 3, 4, 5, 6 pin 15 is not shown, but it should be shown and connected to ground.

3) On IC 4a line is shown going from pin 7 to an undesignated point on IC 8. On IC 8 this point should be labeled as pin 6. "g

You can help this computer,

Or you can turn the page.

ANNOUNCING. ... a

KEYBOARD BEEPER FOR THE ZX80

This low power CMOS circuit ends data entry problems common to Sinclair-style keyboards by beeping when a key is depressed. Fully assembled and fits inside computer.

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Alan Groupe, Michael Tardiff, and Ivan Zatkovich

To Build or not to Build?

A Reveiw of the Sinclair ZX81 Kit

As has already been said in the pages of SYNC and elsewhere, Clive Sinclair deserves some sort of medal for introducing a much improved version of an already popular computer and selling the new version at a lower price. You don't find deals like that often these days, on either side of the Atlantic.

After you decide that the ZX81 is the computer for you, your only remaining decision is whether to save $50 and buy the kit version, or whether to go the fast and easy route and buy a "plug-in-and- run” ZX81.

Should you build your own ZX81? If you've never built anything electronic before, no. If you haven’t used a soldering iron (a small, 25-watt or less, narrow-tipped iron with rosin-core solder) before, no. If your patience is not one of the things for which your friends admire you, no.

But if you’ve built kits before, Heathkit or otherwise, if you can solder with con- fidence, and if you have a couple of spare hours on hand—yes! You can have a good time, save enough money to make it all worthwhile, experience the warm inner glow that comes from using something you assembled yourself, and be reasonably sure that your ZX81 will work the first time you turn it on.

The engineering of the computer is topnotch, as is the packaging. The board is silk-screened and solder-masked, and poses no problem if you have a soldering iron with a small tip and some fine-gauge solder. The instructions for assembly, however, leave a bit to be desired if you like (or need) to have things spelled out step-by-step for you.

12

Getting It Together

Our kit came carefully packed in a plastic foam container, not just thrown in a box. The components were packed in little bags although they weren't grouped in any order that paralleled the assembly instructions. We were told by a friend, however, that his kit was packaged in a large cardboard box rather than plastic foam like ours. (We'll get a third opinion when our other two kits arrive — there are three of us, and one ZX81 can't satisfy all of us at once...)

The assembly instructions aren't Heath- kit-style "step-by-step"; they might as well read, "Put the components in the proper locations and solder them in." If you read the instructions carefully and work slowly, this won't be an impediment. But, if you can't wait, and rush ahead, making assump- tions along the way, you'll blow it, like we did. Since the board uses plated-through holes (the inside walls of the holes are metal-plated just like the traces), it can be frustratingly difficult to remove misplaced components after you've soldered them in.

The instruction sheet starts off by recom- mending that you read all of the instructions carefully. A good idea, but “memorize carefully" is what it should read. The arrangement of the assembly instructions and the "warnings and hints" is such that you must remember the “warning and hints" as you go through the assembly instructions. If the ^warnings and hints" had been mixed in with the assembly instructions, we would have made three fewer mistakes than the three mistakes we made. We didn't have anyone to caution us, though; now that we've told you, you shouldn't have any trouble.

There are many extra "unused" holes on the board (it is common on plated- through boards to use holes to connect traces from one side of the board to the other), and the board is so small and tightly packed that it is easy to place a lead in the wrong hole if you are not careful. A picture

of a completed board showing proper component layout would have been a great help. We've included such a photograph with this article. (Figure 1).

The parts list includes along with the component name (R3, etc.) and the compo- nent value a description of the marking on the components. This is handy for people who may have not memorized the EIA resistor color code, and in identifying some oddly-marked parts (like some of the capacitors that are marked in nanofarads (1000 pf), an uncommon unit in the United States).

Our kit had the correct number of each part, but our friend's kit was missing one memory chip and a resistor, and had two extra transistors and couple of spare resistors of different values. Be sure to check your

Figure 1.

parts against the parts list before you start building — Sinclair will gladly replace shored parts, and it's disappointing to have to stop assembly in the middle to the kit to wait for a part to come in the mail.

The instructions suggest that the resistors are pre-cut and bent, a time-saver to the kit builder. However, both the 470 ohm and most of the 1K ohm resistors come full-length. This, as we discovered ten solder connections too late, is no accident. The pre-cut resistors are installed flat on the board, while the full-length ones are mounted on-end, sort of standing up. While a warning to this effect is indeed contained in the instructions, this warning is not where we were looking when we installed them; hence, we put many of these resistors in wrong and had to make a trip to Radio Shack. Also note that some parts (like

SYNC Magazine

INSTANT INFORMATION WITH

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R30, a 10-ohm resistor) are used in the U.S. version of the kit, but not the U.K. Be sure you've read the instructions carefully to decide which parts are or aren't used. Figure 2 will help you in proper component placement.

Also included are two "resistor packs." These packs have a right end and a wrong end, and must be installed the right way. The instructions state that the common end is marked by a white dot—ours had no dots, white or otherwise, but instead a black square towards the middle but off to one side. No big problem, really — the end closer to this black square is the common end. If the instructions had reminded us, "Install the resistor packs, remembering to place the marked end near the *C" silk- screened on the circuit board," we probably wouldn't have soldered them (both!) in backwards. Desoldering a seven-pin part from a plated-though board, we discovered, is very close to impossible without destroying the part or the board. We had to wait a week for the replacements to come from Sinclair to pay for our error.

We discovered a spare part at the end of our assembly, which we soon decided was the ceramic filter (it looks like a three- legged capacitor). It had been left out of the "install all of these parts" list. The kit won't work without the filter, so you should (as we did) put it in, even though you're not explicitly told to do so.

The installation of the modulator posed a problem we couldn't solve ourselves. According to the instructions, the two leads go in the holes marked Fr/UK1 and UK2. Common sense told us that this may be wrong, since we knew that neither “Fr” nor “UK” have television systems exactly like “US.” We, of course, wanted to use the holes marked “USA,” but there are three such holes and only two leads. We then decided to look at the schematic — wrong move. Apparently there are several versions of the ZX81 kit, and the schematic appears to be an interesting combination of all of them. (Printing one schematic and one instruction set for the world is probably one of the ways Clive manages to keep prices so low...)

Thoroughly confused, we decided to call Sinclair for assistance. They informed us that there are two variations of the kit being delivered to the US—a UHF kit with a two-lead modulator using the Fr/UK1 and UK2 holes, and a VHF kit with a three-lead modulator that uses the “USA” holes. Problem solved. According to our friend, later kits like his are packaged with a supplementary instruction sheet that makes all this clear.

The keyboard for the ZX81 is a self- contained unit, unlike the ZX80's, which used the bottom of the printed circuit board and a stick-on overlay. A thin film with conductors “printed” on it serves to connect the keyboard unit to the computer; this

14

Figure2. 1 — ——sist

film slips into a connector you install on the printed circuit board. It is a good idea to clean the ends of the keyboard connector film before you plug it into its connector. Light rubbing with a pencil eraser will ensure a good connection. Slipping the keyboard straps into the connector proved to be a little tricky, but an even pressure and some verbal urging does the trick.

We checked the voltage produced by the power supply before we plugged the ICs into their sockets, just in case something else had gone wrong in the assembly: we couldn't wait another week for replacement ICs to come in the mail. If you have access to a voltmeter, you can check the power supply by plugging the AC adapter into the 2012815 power jack, then measuring the voltage across pins 2 and 3 (middle and right-hand) of the voltage regulator (which is attached to the metal heat sink). If you find five volts there, everything's ok so far. If you don't happen to have a volt meter, try using the "burnt thumb" method — apply power to the board and place your thumb on the plastic case of the regulator. If your thumb starts smoking, the regulator is using more current than the designers planned, and you probably have a short somewhere. Check your soldering, and look for solder bridges across traces.

Be sure that you unplug the kit before installing the ICs, unless you want to zap a couple chips.

The Moment of Truth

After all our troubles, the machine worked the first time we plugged it in. We put the case together (it's held together by screws instead of these funny plastic things used on the ZX80), plugged it in, and entered our first program. After playing around with our new toy for a while, we became ZX81 converts (and thus our two more kits on the way). Our only remaining question was why Sinclair put the vents on the bottom of the case. Must have been so the heat could fall out.

From start to finish the whole building process took about five hours, including a little backtracking. Considering the $50 savings offered by the kit version, you earn about $10 an hour, have a good time (barring disaster), and end up with a great computer for the lowest price around.

All things considered, the quality of the kit is excellent; Sinclair didn't cut corners anywhere. Everything Sinclair has ever made has been ingenious, well-built, and surprisingly inexpensive, and the ZX81 is not exception. Sinclair remains hard to beat for engineering excellence— but tonight, in Benton Harbor, Heathkit sleeps easy.

[| Authors’ P.S.: Since writing the review, we have received both a UHF and a VHF kit from Sinclair. There are some significant differences between the two which will be covered in a future column.]

SYNC Magazine

Writing For SYNC

Paul Grosjean

If you have material you want us to consider for publication, we are very much interested in looking at it. If it fits our editorial needs at that time, we will send you a "Transfer of Copyright Agreement" to sign and payment for your article. On the average we pay about $20 per printed page in SYNC. When you submit material, we ask that you keep the following in mind:

1) Type your manuscript on standard typing paper (one side only) with at least one inch margins all around.

2) Use the double space setting for your text throughout.

3) If you want your manuscript returned, enclose a self-addressed stamped (do not use a postage meter) envelope. If you want to be sure that we have received your work, enclose a self-addressed postcard.

4) Be sure to put your name, address, and phone number on the top of the first page in one corner. In the other corner put the machine requirements of your article or program (for example, 8K ROM; IK RAM. 8K ROM; 16K RAM. 4K ROM; IK RAM). Remember that our readers have a variety of ROMs and RAMs and they are not happy to find out after they have entered a program that it does not fit their machine. Put the title or a short form of the title on each page in the upper left corner. Paginate on the upper right corner.

5) Type with normal use of capital and lower case letters. Do not type everything in capitals in your text (in programs, however, do use capitals since that is what your computer uses). This applies also to headings and subheadings. Show subhead- ings by leaving extra space above and center- ing.

6) Underlining means that those letters should be italics when printed. So underline only when you mean “Use italics here.”

7) Paragraphs must be indented (5-8 spaces is usual). Do not use extra lines to show paragraphs.

If your article includes programs or listings, please keep these items in mind:

1) We prefer camera ready copy of programs and listings whenever possible because this substantially reduces the risk

January/February 1982

of typographical errors. Carbon ribbon typewriters make excellent copy. Printers and regular typewriters which give a sharp, clear image usually can be used, but make sure that the ribbon is dark. Of course,

when the ZX Printer becomes available in .

the U.S., printouts from it will be acceptable. In addition, we would like to have the programs submitted on cassette with several saves, especially if the program is over 1K.

2) Type the program so that it will look just like the screen display including all spaces that are necessary or that the computer puts in automatically. Do not use extra spaces where the computer does not use them. This is a big help to the reader in checking whether he is entering the program correctly and helps him reduce copying mistakes.

3) Show necessary spaces in PRINT statements with a # mark.

4) Program notes which help the reader to understand what is going on are helpful. These may be given as side notes on the same line as the program line or at the end of the program with line numbers for matching. In either case keep the width of the notes the same as the program listing.

5) If you use graphics, be sure to specify in the notes which key to use to get the graphic.

6) If possible, make suggestions for adapting your program to fit other machine requirements. For example, if you have a program that takes 2K RAM, tell the reader where to shorten it to squeeze it into IK if possible. If you are writing for an SK ROM, supply the changes necessary for the 4K ROM if possible. Readers like to know where they can make changes in the programs to vary the results. Point these out also.

7) Type your program single spaced.

8) Be sure to indicate in your article how to RUN the program and what the reader should expect to see on the screen when he has done so.

9) Follow the emerging conventions for ZX80/81 programs: a) number program lines by 10's unless you have a reason to do otherwise; b) avoid using letters that can be confused with numbers and vice versa;

C) use consecutive designations for strings and variables; d) identify your program with a REM statement.

10) Provide the SYNCSUM (see the Perceptions column in this issue). Other checksums may be used if there is a good reason to do so, but the process for finding them should be explained.

Photos, illustrations, charts, and diagrams usually add to an article. Again, we prefer copy that we can use directly without redrawing. Illustrations can be larger than the expected final form because we can reduce them, but they should not be smaller. All charts, diagrams, listings, illustrations, photos, tables, and programs should be labeled such as Figure 1, Listing 1, or Table 1 and referred to in the text in that way rather than as “the table below” or “the following lines” because we may not be able to do it that way in our layout. It is even helpful to put all the figures, tables, etc. at the end of your article.

If youcan supply your text and program listings on disk, include the information on the type of disk system you have. We would prefer that form if it is compatible with our equipment.

Following these suggestions will help us a great dealin using your material. "a

8K ROM

Ery Eie

This columns will feature short programs to show off your computer, impress your family and friends, and tickle your imagina- tion when $YNC arrives at your place. We invite your contributions. Address them to: Try This, SYNC, 39 E. Hanover Ave., Morris Plains, NJ 07950.

With your computer in SLOW mode, type in: 10 REM YNC and hit NEWLINE Type in: POKE 16513,56 and hit NEWLINE. POKE 16517,147 and hit NEWLINE. Then hit NEWLINE again.

With your computer in FAST mode, type in: 10 PRINT CHR$ (INT (RND*8) +2; 20 RUN

After observing the results, try it again in SLOW mode (hit SLOW and NEWLINE and then type RUN and NEWLINE). Ma

James Grosjean, 50 Kings Road, Chatham, NJ 07928.

15

4K ROM 1K RAM

How to Invent a Game— Inside Flattop Lander (MCD)

"How to make a million dollars and NEVER pay taxes," by Steven Martin. “First. get a million dollars..."

As computerists, the million-dollar ques- tion that you and 1 had after learning 0 fundamentals was, "Okay, now what do I do with it?"

First...Get an Idea

The general idea for Flattop Lander was a natural progression from my other "aircraft" games. Good ideas are all around you take a look.

Probably everyone has seen a movie showing landings on aircraft carriers, whether of WWII propcraft or of modern-

Jonathan Bobst, ZETA Software, P.O. Box 3522. Greenville, SC 29608-3522.

16

Jon Bobst

Figure 1.

Actua

1

Navy jets. There are two images that we retain: the view from the aircraft (pilot's view) and the scene from deck or from another ship. Your first decision after getting an idea is to choose a display image.

For a descent pilot's view sequence with its separate "frames" for a three dimensional effect, several hundred addresses in RAM must be used to store the different char- acters needed. With only 1K of RAM available for both display and basic program, the pilot’s view option is out.

The next best thing is to combine a 2-D display (side-view) of the landing with a routine that requires the player to “get into" the display. [n other words, require an input that involves the player, making him/her construct a mental image or *mind's eye” picture as in Figures 1 and 2.

This “window” is recognizable as the standard 3 x 3 input matrix, but with a 3-D twist: 5 means straight ahead and 9 means

Figure 2.

Mental “Window”

SYNC Magazine

down to the right, etc. The Basic display of Height and Distance are not really necessary, because the player can see his position on screen. But the LINE is not optional — that tells the pilot which way to turn: left “<”, right “>”, or “X” for on- line for a straight landing. (That is part of the deck flagman's job.)

So, in the planning stage for your display, refine your idea to a scene that allows both room for movement and room for the Basic statements and any Basic printouts you may need.

Display Construction

First, you must estimate just how much display you can have— enough to make the "play" visually interesting, but not so much that the program will crash or stop on error code 5 (no more room on screen).

Remember that each space assigned to a screen display means one less address that can be used in the Basic program (and vice versa).

In Flattop Lander, since the last 400 feet in height are the most important to a pilot, the actual "play field" can be set up as 5 rows of 32 spaces for aircraft movement, 1 row for the zero-height of the flight deck and carrier characters, and 1 row of sea surface. Thus, 7 rows of 32 spaces plus 7 "118's" as end-line markers plus 8 “118’s” to move the play field to mid-screen totals 239 addresses — leaving 700+ for the Basic program.

Second, work out how you would con- struct your display in Basic. For Flattop Lander, it would take around 20 statement lines and 2 or 3 seconds in execution time. The obvious advantage of an MCD version is that, while it may take more "know- how" to write, execution time is typically less than half a second...short enough for anyone 5 attention span.

Next, translate your Basic display into Machine Code decimal values.

Z80 Source Coding for Flattop Lander

Figure 5.

Z80 Source

Statement

Decimal Code

Comment

Step 1: Initialize the subroutine with the address held in "D-FILE"

az LD HL, inn) 12 n=12

64 =163596 nó4

36 INC HL.

Step 2: Loop eight times for a column of " 118s" 6 LD Bn

3 n=8

62 LD AWN

117 n=117

60 INC 6

119 LL.D {H.D , A dd INC HL.

16 DJNZ نت‎

(em2589-249)‏ ن

:put display address (DF ILES pinto HL register-pair

sheld at 16396

point to next

Screen

address

put the following number

sinto the b

register/counter

;put the following number ;into the A register

sadd 1 for "116 put number in address in HL

f

into

the

;point to next address

subtract 1 from B and

;zero, jump bac

k

6 values

if not

(to 62)

This roundabout way of loading "118" into a screen address is necessary because "118" in Z80 means "HALT" processing, while in ZX80, it means "end of line." Either way, you

cannot use it in a 1 REM subroutine.

Step 3: Loop six times for 6 rows of 32 spaces (blank play field).

6 LD B,n

ó n=6

197 FUSH BC 6 LD Eri ad nei

e LD (HL) 4n OQ m=O

ed INC HL 16 DJNZ e zl eu

62

117

60) (Same as above) 119

Ded

19.5 FOF RC 16 DJNZ & 240 ر7 1 حدم‎

Step 4: PRINT 1 row of sea surface, CHR$(11)

& LD Bah ud ni

34 LD (HL) ari 11 n=11

INC HL‏ كك DJNZ e‏ 16 e=4‏ 251

y

117

60 (Same as above) 119

e

B is row counter

sput the number 1 "Save" stack ŞEK is now free ;put chr code chr code :point to next

1s

;decrement B and

*:minus 4

value

4 ede as

put number

sand jump back

sload B with 32 :load screen

spoint to next ;sSubtract, test

backwards 4 values

:for end of

to next MCD

spoint after

Step 5: Reset system variable addresses and exit subroutine.

to count into Tut

ir

cA

(to

above but

saved into the B register,

lt

EB

Screen "space! Gcrm een Jump

into the SPACES acci essc 0 address Norn- 7 ero

24)

for

Ori

not

address

the

with

1-"118"

stack subtract i Q ito 197)

chr "ri

addr ess and

"

line

address

(to

not-o a4)

jump

"118"

available

A4 LD CRED o HL load the last address in Hl. (4K/1K) . . 14 =] 5598 n=14 pinto both "DF-EG" This subroutine produces instantly a tq (DF-EA) 5 blank field and 1 row of seasurface char- 34 LD (nn), HL sand "DF-END" acters. The aircraft and carrier will be — 16 — «16400 n=16 POKEd in later via Basic, enabling move- " er Tu nec MEDIAM . . es DA, r load A with the row number ment experiments of the aircraft and/or 2 AM سان الب‎ D : . . d n= safter MCD (22-15-8 for F.L.) carrier. The idea is to produce 239 spaces 50 LD inm), A :;put that row number into 16421 on Screen quic kly so that by POKEing dl nsi meaning 88 is the next available only 9 characters in different places, the — | mow hole display will be accomplished in the £f, 71645! ied W play p atri RET return to Basic program

minimum of time. See Figure 5.

January/February 1982

Entering and Testing an MCD

Count the number of values in the subroutine (55 for Flattop Lander) and enter that many "boxes" into line 1:

1 REM LILILI etc. :L] = shifted A

You can use any character, or even 1, 2, 3, etc. The idea is to reserve some non- changeable addresses so they can hold MC values. The first box's address is 16427. (16424—21, 16425—0 16426=254 or “REM”.)

Line 2 in Flattop Lander holds 8 boxes in REM for storing carrier characters. Otherwise, use 2 REM B as a buffer against accidently moving the cursor to line 1: that's a big “no-no” after you enter the MC values!

Okay, you have 1 REM with a line of boxes and 2 REM with either more boxes for character storage or "B" for buffer. The next step is to scroll line 1 off-screen. "How?" you may ask. “I only have the 4K chip."

You do not need the 8K ROM chip to scroll one of only two lines off screen, and you do not have to enter a lot of “dummy PRINTS" as bulk, either.

NEED MORE MEMORY?

for your ZX80/81

EXPAND IT TO:

16K Memory

32K Memory.............

48K Memory. ..... $259

Plus 5.95 shipping/handling. Mass. resi-dents add 5%.

OUR 16K/32K UNITS ARE EXPANDABLE!!

Systems are assembled & tested.

RKL SYSTEMS

P.O. Box 515 Leominster, Mass. 01453

18

Here is the trick — with the cursor below line 1, enter this command on the edit line:

POKE 16403,2 and ZAP!, line 2 is now at the top and line 1 is off-screen. (Look on page 122 of your ZX80 manual for the reason it works. Hint: 16404 always contains 0 when the line number is less than 256.)

Now enter the input routine to POKE the 1 REM boxes with MC values. See Figure 3.

If you write down your MC values in a 4-column table (read left to right) and then “INPUT” from it, one 4-value row at a time, it is easy to spot entry errors.

GOTO 100 and enter the MC values, then SAVE on tape in case of entry or coding errors. Lastly, on the edit line:

LET Q=USR(16427) and BINGO! your initial display springs instantly to life from a lot of no-longer- mysterious numbers.

Well, maybe it doesn't...in which case, unplug your “crashed” Z X80, plug it back in to reset the ROM from hardware, LOAD the partial program, and edit out lines 110 and 120. GOTO 100 for a complete printout of the MC code table and look for entry error. If none, recheck the decimal values of your subroutine. (My usual mistake is to miscalculate the offset values for DJINZ and other "Jump Relatives.")

Now that you have an instant MCD, you have to POKE some characters into it. If you use 2 REM for character storage, you can use the same input routine by changing line 100. Add 5 to the address of the last box in 1 REM for the address of the first box in 2 REM. Flattop Lancer has eight characters in 2 REM, so line 100 is FOR X-—16486 TO 16493.

Finishing an MCD with POKEd Characters

For reasons of scale and lack of RAM, only one character is used for the aircraft in Flattop Lander: 277, or a period. 20, ora “- looked better airborne, but not landed. The more characters you have moving around the screen, the more complicated and lengthy your Basic POKE-routine will be.

How the game's display is tied together is shown in Figure 4.

Before and after the above statements are game routines for entering values from the input matrix and changing the value of "C"; one line to assign a random value to “L” as “wind current”; lines to calculate Height, Distance and which way to turn to stay on the approach Line; a Score, Crash, or new-approach input routine; and an end-game/exit routine, all in Basic. That sounds like a lot of processing between displays, but "flicker" time remains under half a second! See the advantage of an MCD, now?

For your own games, you can invent or modify displays and rules to suit yourself. In this way you can see one of the best reasons for buying a microcomputer rather than a “game machine." With a computer, you are not restricted by someone else s viewpoint of what is FUN.

In Part 2, we will see how to develop "game" routines in Basic that will make your program do what you want it to do.

Fa

Figure 3.

100 FOR X=16427 TO (16427*0X-1)) 110 INFUT Y 120 POKE X,Y 130 PRINT FEEK ) NEXT X

OD,

$XX-the number of MC values SFLATTQOF LANDER = "TO 16481" this loads the box w/value

stor a 4-column "running" display pot POKED address-values

Figure 4.

40 LET Cr? 90 LET GsUSR(CL&dq:27)

LET P=PEER (16396) +PEEK (16597) X256

110 FOKE P+163,132 120 LET Y=16486

130 FOR X=P+193 TO P+200

140 FOKE X,FEEE CY)

150 LET Y=Y+i

160 NEXT X

170 POKE F+C, 27

180 PRINT "HT","DIST","LiNE"

:7 added to CALL

: n E it

"RY = dst field subroutine in 1 REM

= Oth address of screen display

S132 15 "bridge"

SY = first address in Z REM restart carrier at 1923rd space

$s"print" chr held in 2 REM point to next chr address

addi.

chr of carrier

aircraft position and chr sist of X Basic print lines

SYNC Magazine

eo

UZZIES عه‎ proolems

A Rectangular Problem

et’s start off with a simple (?) counting problem. As in all puzzles of this nature you only get one chance so study the

diagram carefully. Your problem is to ascertain how many rectangles are depicted in the illustration at the right. Are there 12? Are there 20? You have five minutes to decide.

Who's Who?

hree couples are out playing

tennis at the Shady Knoll

country club. The names of

the players are Fred, Tom,

Joe, Mary, Nancy and Patty. Joe and his sister are sitting out the first game while Fred and Tom's wife are pictured here playing against Mary and Nancy's husband. From your van- tage point at the side can you tell who is married to whom?

The “26” Puzzle

an you place the numbers 1 through 12 in the 12 circles that go to make up the star pictured at the right in such a manner that the

values in the four circles, in each of the six rows or circles, add up to 26?

A Word Square Problem

GEORGEN

RERENTS ood word-square puzzles are few and far between. Below we have LESSTEN pictured seven seven-lettered words. The letters in each word have RATRIOT been jumbled about. Your problem is to sort out each word and then RANDEN rearrange the words top-to-bottom so as to form a “word-square”; TOS MOX E AO that is, the words in each row will also be spelled out in seven RENTGAS

columns top-to-bottom.

The Flock of Geese

wo friends, passing a woman with a flock of geese, made a wager as to who should guess nearest

at their number, without actually counting, one maintaining that there were not more than thirty, the other that there were over forty. On asking the market-woman which was right, she replied, "If I had as many more, and one-half as many more, and one-fourth as many more, I should have one short of a hundred. Now puzzle it out for yourselves." What was the number of the flock? (This puzzle is from that great old Victorian puzzle book Puzzles Old and New by Professor Hoffman)

That's it for this issue folks. Remember, if you have any puzzles that you would like to share with the readers of SYNC send them in, and, if Merlin uses them, he will send you a copy of one of his famous Merlin 5 Puzzler books.

Your Editor, Charles Barry Townsend سے‎ Answers on page 33. 7 er 4 A, >

January/February 1982 19

The Game of Life Revisited — An Assembly Version

Richard Booth

The Game of Life, printed in SYNC 1:2 (pp. 28-30), was written in Basic. This Basic program may be replaced with an assembly subroutine which displays each succeeding generation within a fraction of the time needed by the Basic program. Each generation is constructed and then displayed by using another assembly sub- routine for creating a display file based on "A Display File in Machine Code" by Dr. I. S. Logan in the same issue (pp. 13- 15).

Program to Enter Assembly Subroutines Figure 1 is a listing of the program for entering the Hex formatted assembly instructions. Line 100 contains the space which will be occupied by these instruc- tions. As always, once the subroutines have been entered, do not LIST the pro- gram because the system will hang up. The assembly routine is entered one byte at a time. A backspace character, “/”, is provided in case an error is made in entry. This backspace can be used more than once. When the subroutine is com- pletely entered, type in "END" to stop.

Assembly Subroutines

Figure 2 is a listing of the display file subroutine adapted from Dr. Logan's article. When the routine is RUN, the

display will show a palette of 10x30 loca-

tions surrounded by a border.

Richard Booth, 12875 Highland Rd., Highland, MD 20777.

20

— — Figure 1: Program to Enter Hex Format.

100 REM [247 shift D's]

200 LET V=-1

210 LET V=V+1

220 IF (V/50)*50— V THEN CLS

230 IF (V/10)*10— V THEN PRINT

240 INPUT H$

250 IF H$—"" THEN GO TO 240

260 PRINT H$;"zz";

270 IF H$=“END” THEN STOP

280 IF H$=“/” THEN GO TO 310

290 POKE 16427+V,16*CODE(H$)+CO DE(TLS(H$))-476

300 GO TO 210

310 LET V=V-1

320 GO TO 240

Figure 3 is a listing of the Game of Life subroutine. Its structure, similar to that of the Basic Game of Life, is shown in flowchart form in Figure 4. The rules for the birth and death of cells are the same as in the Basic version.

Entering the Program

After entering the program in Figure 1, type in the Hex Format column in the Display File subroutine in Figure 2. Type ‘END” when this has been done. To check to see if this has been correctly entered, type LET A USR(16427). The palette should appear immediately. If it does not, check the program.

Figure 2: Display File Assembly Subroutine.

Decimal Hex Label Mnemonic Hex Address Address Format Format 16427 4028 START LD HL,(D-FILE) 2A OC 40 E INC HL 23 F CALL EDGER CD 57 40 4032 LD B,10 O6 OA LINE PUSH BC CJ 5 LD (HL),9 36 09 7 INC HL 23 8 LD B,30 06 1E A SPACE LD (HL) ,O 36 00 C INC HL 23 D DJNZ SPACE 10 FB F LD (HL),9 36 09 404] INC HL 23 2 CALL DLIM CD 5E 40 5 POP BC Gl 6 DJNZ LINE 10 EB 8 CALL EDGER CD 57 40 B END LD (DF-EA) , HL 22 CE 40 E LD (DF-END) , HL 22 10 40 4051 LD 4,1 3E OB 3 LD (LINE-CTR),A 32 25 40 6 RET C9 7 EDGER LD B,32 06 20 9 EDGE LD (HL),9 36 09 B INC HL 23 DJNZ EDGE 10 FB E DLIM LD A,117 3E 75 4060 INC A 36 1 LD (HL) ,A 77 2 INC HL | 22 3 RET C9

SYNC Magazine

diis.

Figure 3: Game of Life Assembly Subroutine.

January/February 1982

Mnemonic Format

LD IX,0023H (408CH)

LD BC, ADD IX,BC PUSH IX

LD C,0AH

LD B,JLEH

LD 2,1

LD A, (IX-@1H) CALL TEST

LD A, (IX+@1H) CALL TEST

LD A, (IX-20H) CALL TEST

LD A, (IX-21H) CALL TEST

LD A, (IX-22H) CALL TEST

LD A,(IX-2f8H) CALL TEST

LD A, (IX-21H) ADD D

LD (IX*00H),A INC IX

DJNZ LOOPX DEC C

JR Z,A

INC IX STSCOR INC IX

INC IX

JR COUNT

POP IX

LD C JAR

LD B,1EH

LD A,(IX*00H) CP 03H

JR Z,C0ELL

CP 82H

JR Z,CELL

CP 83H

FR Z,CELL

LD (IX4*00),090 JR CELL41

LD (IX400),00 INC IX

DJNZ SCORE DEC C

JR Z,SREND INC IX

INC IX

JR BGNROW RET

CP 5FH

RET M

INC D

RET

LD HL, (400CH) INC HL

CALL EDGER LD B,0AH PUSH BC

LD (HL) , POH INC HL

LD B,1FH

LP (HL),€0 INC HL

DJNZ SPACE LD (HL), øØ9H INC HL

CALL DLIM POP BC

DJNZ LINE CALL EDGER LD (40@FH) „HL LD (4010H),HL LD A,fBH

LD (4%25),A RET

LD 8,1

LD (HL), 911 INC HL

DINZ EDGE

LD A,75H INC A

LD (HL),A

INC HL

RET

Starting address 16498 decimal.

Comment

;Display File Address

;lst PALETTF LOCATION ; 10 Rows ; 30 Rows

;Begin Search for Neighbors ;Call TEST routine

;Call TEST routine ;Call TEST routine ;Call TEST routine

;Call TEST routine ;Call TEST routine

¿Call TEST Routine

;to LOOPX for next Row ;Last Row?

;Finished Search, STart 500816

;lst PALLETTE LOCATION ;10 Rows

; 30 Columns

;Memory Location

;No cell, 3 neighbors ;To CELL

;Cell, 2 neighbors

; To CELL

;Cell, 3 neighbors

sTo CELL

;No Cell

;Skip over CELL ;Create Living Cell ;Next Location

;To SCORE if not end of row ; Row counter

;Last Row?

;Next Row

;Back to Basic

;Living Cell?

;Return to Counting if no Cell ;Increment counter

;Return to Counting

;Display File address

;Call Edge Routine

;Loop to SPACE

;Row Delimiter

;Line

; Edge Routine ; (DF-EA)

; (DF- END)

;Line Counter

;Loop to EDGE ;Row Delimiter

Next, in line 290 change 16427 to 16498. Run the program again and enter the Hex Format column in the Game of Life sub- routine in Figure 3.

The Basic Portion of the Game of Life program is listed in Figure 5. The first part of this program is also from Dr. Logan's article. Replace lines 200-320 of the pro- gram entered from Figure 1 which are already in memory by entering lines 200- 320 in Figure 5.

If possible, save this result. Errors may be corrected either by POKEing or by starting again.

Larger Field for Larger Memories

For readers with additional memory a larger area can be created. For example, a 20x30 field can be created by:

1) Load the program.

2) Change line 240 to read "...A —0600

3) POKE 1635,20 POKE 16511,20 POKE 16589,20

4) SAVE the result.

— Figure 5: Game of Life — Basic Portion.

100 REM, [Assembly Programs|

200 LET A=USR(16427)

210 PRINT "PRESS NO. OR 0”

220 INPUT A

230 IF A=0. THEN GO TO 280

240 IF A-— 1 OR>A 300 THEN GO TO 220

250 LET A=PEEK(16396) + PEEK (1639 7)*2564+ 344A + ((A-1)/30)*3

260 POKE A,-128*(PEEK(A)=0)

270 GO TO 220

280 PRINT “PRESS NEWLINE”

285 FOR I=1 TO 100

290 LET A=USR(16498)

300 INPUT A$

305 IF A$=“S” THEN STOP 310 NEXT I

320 STOP

Running the Program

After “RUN” has been typed, the display palette appears. Enter a starting generation by typing in position numbers as in Dr. Logan’s article. When the starting con- figuration is complete, type “0” NEWLINE, to display the second generation. Each succeeding generation is displayed by typing NEWLINE. To stop the program, type "S".

A random starting generation may be entered by using the lines in Figure 6 as replacements in Figure 5.

Figure 6: Line Replacements for Random Start.

210 FOR 1-1 TO 100 220 LET A=RND(300) 230

270 NEXT I

21

ف جف ي anume.‏

a a

|

Some Good Starting Generations

To begin your exploration of the Game of Life, try entering some of the following generations. The reason for my name choices should become evident.

“Migrating L”: 50,79,109,110,111

"E-Lights": — 135,136,137,138,139,165, 167,169 |

"Hawk": 74,77,104,105,106

"D-Hive": 0162, 190,191

"Melting Snow": 100,101,102,103,104, 130,132,134,160,161,162,163,164

Watch especially the interaction between the different colonies and the borders. Different starting generations will create different succeeding patterns depending upon where they are placed within the palette.

For 8K ROM/16K RAM

This assembly version of the Game of Life may also be implemented on 8K ROM/16K RAM machines. Since there are quite a few changes, the entire revised listings are given below in Figure 7. The program to enter Hex format (Figure 1) may be used with the following line replace- ments:

220 IF INT(V/50)*50— V THEN CLS

230 IF INT(V/10)*10— V THEN PRINT

290 POKE 16514 V,16*CODE 115+ CODE H$(2 TO 2)-476

Use this revised hex-loading program to enter the assembly subroutines listed in Figure 7. Then type in the Basic program listed in Figure 8. The program does not need to press NEWLINE for each succeed- ing generation to be displayed, since a pause is taken between each display.

A next-generation version of the Game of Life might make use of pixel graphics, and a non-flashing display. This would effectively quadruple the “world” size, and some very complex patterns could be observed. "

Figure 8. Game of Life Basic Portion (8K ROM)

1@@ REM RSSEMBLY PROGRAM a LET RA=USR 15514

210 PRINT “PRESS NO. GR &" 220 INPUT A

23 THEN GOTO 258 24@ IF A<i OR A>6@Q@ THEN GOTO 2

BE 250 LET R=PEER (1609851 +PEEK (16 SS7) *2564+347A+INT ( tA-1) 730) #3

= POKE A,12&8s (PEEK (A? =Q) GOTO 220

mÁmogoc-o

Ld Gd ا‎ FO fO fi شم‎ GO Co 4 On

FOR I-1 TO iaea @ LET R=USR 16562 e PAUSE 4a @ NEXT I e

STOP

Figure 9. Line Replacements for Random Start

(8K ROM) S18 FOR I-1 TO 100 220 LET RH-RNDx300Q-150 230 ELETE] 270 NEXT I 24

Decimal Address

16514

Figure 7. Game of Life Assembly Routine (8K ROM; 16K RAM)

Hex Label Mnemonic Hex Address Format Format 4082 START: LD HL,(D FILE) 2A OC 40

E INC HL 23

6 CALL EDGER CD A3 40

9 LD B,20 06 14

B LINE: PUSH BC C5

C LD (HL),8 36 08

E INC HL 23

F LD B,30 06 1E 4091 SPACE: LD (HL),0 36 00

3 INC HL 23

4 DJNZ SPACE 10 FB

6 LD (HL),8 36 08

8 INC HL 22

9 CALL DLIM CD AA 40

G POP BC Cl

D DJNZ LINE 10 EB |

F CALL EDGER CD A3 40

Figure 4: Flowchart for Game of Life Subroutine.

IX <— 35 BC <— (D-FILE)

(A = 130) or (A = 131)?

TEST EACH SQUARE AROUND SQUARE tt IX INCREMENT D FOR EACH "NEIGHBOR"

A €— (IX) A <A+D

(IX) > A

SYNC Magazine

Decimal Hex Address Address

S S

J a » 00 -3 دما ها‎

O ود‎ tj

408

16562

+

O

N e 8 ij OQ O AW لمحم ن- حرا كه‎ O E حزان‎ CN نم‎

ج O‏

X O

€ H tz gj On

FN

+1}

412

COMO ين‎ NO VA V "1 CJ t) OU

413

نم حم ON‏ فقا بو هك 9

January/February 1982

Label

EDGER: EDGE:

DLIM:

LIFE:

LIZZ XXXX :

TCTT:

59555 : TEST:

Figure 7 continued

Mnemonic Format

RET LD B,32 LD (HL),8 INC HL

LD A,(IX«32) CALL TEST LD A, (IX+33) CALL TEST

DJNZ VVVV DEC C

JR 5 INC IX INC IX INC IX

JR TTTT

Hex Format

DD 21 23 00 ED 4B OC 40

DD 7E FF CD 39 41 DD 7E 01 CD 39 41 DD 7E EO CD 39 41 DD 7E DF CD 39 41 DD 7E DE CD 39 41 DD 7E 20 CD 39 41 DD ?E 21 CD 39 41 DD 7E 22 CD 39 41 DD 7E 00

DD 77 00

Glitchoidz heport

GRA+PIX (1:4)

p. 13, right column, 2nd paragraph, last sentence should read: “If P—0 the routine will PLOT; if P=1 it will UNPLOT."

pp. 14-15 all equations with the variables 01,02 (zero) should be rewritten as O1, O2 (letter O).

p. 16, listing 5: add:

9010 REM ENTER FROM POLYGON/ SEGM ENT/ARC

This line does not affect the running but it changes the SYNCSUM.

Change:

9920 IF P2—2*PI THEN LET P2+P2-2 *"PI*INT (P2/(2*PT)) 9925 IF T2—2*PI THEN LET T2=T2-2 *PI*INT (T2/(2*PD)

"Mini-Billboard" for 8K ROM (1:5, p.2) 20 LET A(I)=(CODE(A$)*8) +7680

21 LET AS—AS(Q TO )

50 FOR Y=0 TO 7

70 IF C>=E THEN. GOTO 100

Note: To use the full 8 letter capability of the program you will need additional RAM.

The PEEK Function and POKE Command (1:5, p. 22)

In the note at the bottom of the listing, 129 should be 120.

An Inventory System (1:6) p. 30: 620 FOR B=1 TO 150 130... "ZZUNITS." p. 31; 1780 IF W<>1 THEN GOTO 6 1830 LET IS(B)—IS(B- 1) 3068 IF C$=M$(B) THEN GOTO 3100

The Hidden Chessman (1:6, p 43)

50 LET Q=PEEK(16396) +256*PEEK ( 16397) +2*X-14+34*(Y-1) n

25

Software Review

You May Fire When Ready, Gridley!

John Sampson

Have you ever wished that you could command a submarine, survey the sea through the periscope to locate the enemy fleet, and give the orders to fire your torpedos at the target ship? Well. now thanks to the ZX80 and the Torpedo Alley program from Zeta Software you can do just that, and for very little money.

You get this program, as you do all the Zeta programs, in typewritten format with the listings, directions, and explanations of how the program functions. This three page program has two parts: the Basic program and a machine code routine which, once entered, resides in a REM statement so that you can save and load the program with ease.

After entering the program, which is very nicely documented with comments on the right hand side of the page throughout the listing. a command of GOTO 100 produces a screen display of the view through your periscope. Each press of NEWLINE moves a destroyer from right to left across your periscope viewscreen. When you decide to fire a torpedo, you press T and NEWLINE. The torpedos leave trails through the water as they streak toward their targets. If your aim is good, the target ship explodes; if you miss, the torpedo explodes harmlessly in the water or resets the display to the next ship.

Now what would you expect to pay for such a program? $20? $10? Would you believe . . . $2? That is right! All of Zeta

John Sampson, 23-51 123rd St., College Point, NY

11356.

26

cane SC e

Software's programs are very reasonably priced. Their catalog includes utility, educational, and game programs. A mini- mum number of listings is required per order and $2.50 extra for shipping and handling. Most of their programs are available also on cassette for $5 additional per order. 8K ROM and l6K RAM programs are also now available.

Torpedo Alley does have two limitations which some users may feel. First, the program does not keep any score of how many ships pass, how many torpedos you fire, or how many ships are destroyed. Second, because the program uses only four random speeds for the ships, you learn very quickly which ships to fire at for a hit. But, even with these limitations in 1K, the program is very enjoyable, and some of you with 16K RAMS will, Iam sure, expand the program, as I intend to do.

An example of Zeta's utility programs is The ROM Reader for $5. This program will, when used properly, disassemble the ROM or any machine code program. It requires a rather large amount of typing, so it should be saved several times during entry.

If you have only 1K of RAM, you will have to make several programs and use each in turn to get some of the disassembled statements each time. If you have 16K, you can make a simple change in the program and get it to return all 696 Z80A instructions. The program displays 10 bytes at a time and takes a little while to run, so you must be patient.

When you run the program, you must enter a starting address in decimal. The display will show the address of each byte in decimal, the contents of each byte in decimal, and the disassembled statement for each byte, such as, LD BC,NN or JP NN. When the content of a byte isa number which is being acted upon by the preceding instruction, then the disassembled instruc- tion for that byte should be ignored. As I mentioned before, this program is for the serious devotee, and the average user will find it challenging. However, it is an excellent program for someone who has some understanding of how machine code works. The program has a search routine using the information in REM statements which works beautifully although it takes a while to run.

These two examples of programs illustrate the solid but inexpensive programs available from Zeta. a,

SYNC Magazine

Hardware Review

MicroAce Video Upgrade

Smooth flicker free graphics has been the “impossible dream” for Sinclair ZX80 or MicroAce owners, at least until recently. It has been particularly frustrating to have the new 8K ROM and realize that this capability exists on the chip but is denied the ZX80 user! The MicroAce Video Upgrade was designed to eliminate this problem, and it works very well.

The Upgrade comes as a kit with a high quality PC board, a sack full of parts, and some instructions. These are a bit sketchy but the board layout is clear, and, if you have some exerience selecting and assem- bling electronic components, you should have no trouble although it is certainly not a “Heathkit.”

Installing the kit is another problem. I assembled the board in less than an hour, but spent several days figuring out where to put and how to attach it. It will not fit inside the ZX80's case and some provision for mounting must be made. I placed mine in an external chassis box which also houses my keyboard beeper and connected that assembly to the computer with 14 conductor ribbon cable. The electrical problems 1 had with the Video Upgrade stem from the fact that I have a VHF modulator in my system. Installation procedures for these differ from those equipped with UHF modulators and the differenes are not adequately explained. After some false starts and some unnecessary board surgery, the following was determined:

a) If you have a VHF modulator do not make the indicated cuts between:

1) IC21 pin 1 and IC19 pin 5 2) IC19 pin 5 and R324 35

b) Do make the indicated cut in the SYNC track (IC19 pin 6 and the base resistor at TR1).

c) The indicated connection between IC21 pin 2 and R32 35 is unnecessary.

Tom Keeney, 9629 Dortmund Dr., Huntsville, AL

35803.

January/February 1982

Tom Keeney

You should also be prepared to build a simple buffer circuit for the output of the Video Upgrade. The circuit for this is shown adequately in the instructions. However, you have to get the parts from Radio Shack and no mounting provisions is made on the PC board. I installed mine in the 14 pin dip socket interface.

After assembling and installing my Video Upgrade kit, I applied the power and it worked the first time although an adjustment was required to center the K vertically inside the cursor. My characters were actually split horizontally and rolled verti- cally so that the middle of the cursor was a space with the bottom of the K at the top and the top of the K at the bottom. The adjustment is to be expected and is ade- quately explained in the instructions.

In operation the Video Upgrade is great. The SLOW and FAST commands work exactly as described in the 8K ROM manual.

With the modification, the ZX80 produces pleasant, flicker free displays and smooth animation in the SLOW mode. It is, however, awfully slow. The only solution to this appears to be machine code graphics. The only lingering peculiarity is the fact that the top row of print is inclined slightly to the right (this occurs in the SLOW mode only; PAUSE or FAST displays are entirely normal). MicroAce says that fixing this would require a complete redesign of the ZX80 board. The distortion is, in my opinion, a very minor problem.

Since I installed the Video Upgrade, my software has become increasingly display oriented. Even if you are not interested in “games,” the MicroAce Video Upgrade is worthwhile modification to your Z X80. It

will turn it into a ZX81 for only $29. Quite

a bargain! L

DEALER INQUIRIES WELCOME

“THE SOURCE" For:

Personal Computer Software, Books, Games &

Accessories DEPT. C9, 1025 INDUSTRIAL DR. BENSENVILLE, IL 60106-1297

/D board

for Microace, ZX-80,81 16K RAM

edge connector

Programmable 8255 P.I.A. can be configured for direct I/O; polling of peripheral devices,

vectored priority interrupts. Use it with A/D converters, serial I/O port chips, relays, sensor inputs, clock chips, ora security system. Play chimes with different tunes using your computer. 8080 M/L programs, TRS-80 M/L programs will work. Literature available with experiments, programs, and information on how to use the

8255 PIA. Basic 8255 board $50

add-ons extra

Professional Electronics 109 CHESNEY LN., COLUMBIA, S.C. 29209

27

Hardware Helpers

Daniel E. Schaaf

Hardware Relief from Crashes

After many a POKE where I should not have been POKEing, the ritual of unplugging the ZX80 to restart became a chore. It may seem silly, but there may be some PEEKing and POKEing programmers who do not know that a reset pin exists on the Z80 microprocessor. After several bouts with crashed programs l gave in and placed

Figure 1.

On the MicroAce, the capacitor is C2. For both computers, it may be easiest to solder to R4.

+5V. | e * R4 000

4 10K*

T—

m *Add for 1 restart

a push button switch and resistor as shown in the drawing on my ZX80. Since | drive my monitor directly 1 had removed the modulator long ago and put the bright red button nicely in the RF out hole. Now when programs fall into the black hole of endless, breakless loops, 1 press the big red, and relief is milliseconds away. Mg

Daniel E. Schaaf, 306 N. Carroll Ave., Michigan City, IN 46360.

28

High Contrast Inverse Resolution

One disappointment 1 had with the ZX80 was the compromise which had to be made between resolution of inverse video char- acters and the contrast or sharpness of the screen. 1 drive a cheap tube TV set directly as a monitor and the only way to maintain readability of the cursor was to set the contrast low. The following idea helped eliminate some of that problem and opened new graphics potentials.

By placing a 5K resistor and diode between the video out (before the modulator at the junction of R30, 32) and pin 4 of IC- 20 (see drawing below and schematic as published in SYNC 1:1) everytime an inverse character is printed a small amount of white is added to it thus lifting the inverse video out of the soup even in high contrast situations. An added bonus is that inverses are no longer exactly inverse. Graphics

now have a pleasant variety of four shades of grey. The effect on some graphics is the illusion of depth or texture. Another feature is that this resistor/diode can also be used to. probe the timing of events within the display field by terminating the diode at various points within the computer instead of at the pin mentioned above. A variety of masks, field patterns (mostly from the refresh cycle), and other video goodies exists within. One mask in particular, if shifted four clock cycles later, shades the text thus aiding readability. Another blocks out the main graphics area whether or not the field is occupied. The smaller the resistor's value the blacker the masks and patterns become. If too small, however, a crash is possible. The greatest use to me of this mode has been is unlocking event timing within the ZX80. "n

Figure 2.

Make as short as practical

| ريد

Pin 4 (May wish to solder on board, not IC)

2-10K Resistor

Switching diode

Crystal

SYNC Magazine

2 d

ca " al* s

Fred D'Ignazio and Stan Gilliam have . created a delightful picture book adven- ture that explains how a computer works toachild. Katie "falls" into the imaginary land of Cybernia inside her Daddy's home computer. Her journey parallels the path of a simple command through the stages of processing in a computer, thus explaining the fundamentals of computer operation to 4 to 10 year olds. Supple- mental explanatory information on com- puters, bytes, hardware and software is contained in the front and back end

papers.

Cana computer mow your lawn? Not yet.

But a flowchart can show you how to make money cutting five lawns a day. The flowchart is easy. Mowing the lawns is still hard work.

Dr. Sylvia Charp and Marion Ball wanted a way to introduce basic computer concepts to children in grades 5 to 9 of the Philadelphia City Schools. So they identified some tasks that kids understood like mowing lawns, issuing paychecks and controlling traffic lights. They showed how computers are used in these tasks.

` new friends

A A to your child...

Katie and the Computer

Thrill with your chidren as they join the Flower Bytes on a bobsled race to the CPU. Share Katie's excitement as she encounters the multi-legged and mean Bug who lassoes her plane and spins her into a terrifying loop. Laugh at the madcap race she takes with the Flower Painters by bus to the CRT.

"Towards a higher goal, the book teaches the rewards of absorbing the carefully-written word and anticipating the next page with enthusiasm..."

The Leader

"Children might not suspect at first there's a method to all this madness—a lesson about how computers work. It does its job well."

The Charlotte Observer

*...the book is both entertaining and educational." Infosystems

Flowcharts - A basic concept

They devised flowcharts. They located scores of photos. And they found anartistic high school student to illustrate these con- cepts with lively full-color drawings.

They then wrote a light-hearted but infor- mative text to tie it all together. It talked about kinds of computers, what goes on inside the machine, the language of the computer and how computers work for us.

Theytookthe problem of averaging class grades and showed how a simple yrogram could be written to do this job.

Well-qualified authors Marion Ball has written other books on

computer literacy. Sylvia Charp is the director

of educational compuuting for Philadelphia

City Schools. They pooled their talents to

produce this book, Be A Computer Literate.

This easy-to-read book explains how com- puters are used in medicine, law enforce- ment, art, business, transportation and ed- ucation. It's interesting and understand- able.

Computer ret ete

Order Today

Katie and the Computer is hardbound, illustrated in full color throughout and costs just $6.95. A T-Shirt picturing the program bug in the story is also available (purple bug on a beige shirt). Shirts are available in adult S, M, L, XL, children’s S, M and L and cost just $6.00.

To order send payment plus $2.00 postage and handling per order to the address below.

creative competing

Dept. Z0121 One Park Avenue, Room 458 New York, N.Y. 10016

*Residents of CA, CO, DC, FL, IL, MA, MI, MO, NJ, NY State, OH, SC, TN, and VT, add applicable sales tax.

Too much demand

The Bell System distributed 50,000 copies to schools throughout the U.S. but they couldn't meet the continuing demand. So Creative Computing Press now distributes the book. Order yours today. If, after reading it, you do not feel that you are “computer literate," return it for a full refund.

Send $3.95* plus $1.00 postage and handling to Creative Computing, Dept. ZO1 20, One Park Avenue, Room 458, New York, NY 10016.

creabive competing

*Residents of CA, CO, DC, FL, IL, MA, MI, MO, NJ, NY State, OH, SC, TN, and VT, add applicable sales tax.

8K ROM 1K RAM

Part 1

Understanding Floating-point Arithmetic

The aim of this article is to give the reader some insight into the complex world of floating-point arithmetic. Since the 4K ROM provided only integer arithmetic, readers who possess only this ROM will be unable to try the programs. Nevertheless they will be able to follow the text.

In the Sinclair Manual, ZX81 Basic Programming, chapter 27, Steven Vickers shows that a floating-point number consists of a single exponent byte and 4 mantissa bytes, but he gives no further information. In order to understand this subject it is probably best to return to first principles — so with pencil and paper to hand proceed.

Decimal format

In the beginning there were only simple integers. But soon they begat decimal numbers, which have an integer part, a decimal-point and a decimal part. And in their turn decimal numbers begat E-format, which has a mantissa part, an ʻE’ and an exponent part.

For example, the number 'four' can be expressed as:

4 - its integer value

4.000 - its decimal value

40000E-4 - just one of many E-format choices

It can readily be seen that in the E- format we have the essential parts of floating-point notation for decimal numbers all given, but it is useful at this point to

Ian Logan, 24 Nurses Lane, Skellingthorpe, Lincoln LN6 OTT.

30

introduce two conventions that will help us in conversion from decimal-floating- point to binary-floating-point.

1) Always express the mantissa starting with the decimal-point.

2) Do not attribute a sign to the mantissa. Simply state whether the value is positive or negative. So instead of:

Write: 40000E-4 .4 1 & positive 0.00678 .678E-2 & positive -223.9 .2239E3 & negative 0.7 .7E0 & negative

These conventions can be considered to be ‘normalizing’ the floating-point decimal number.

With a decimal number in its ‘normalized’ form we can now state that the mantissa is the decimal part of the form and the exponent is the integer part after the ‘E’. The exponent is a signed integer and the overall form is either positive or negative. Consider the examples in Figure 1. The

lan Logan

will now have to convert the above con- clusions so that they apply to binary-format numbers.

First, consider the state when all binary numbers represented integer values, that iS:

Decimal Binary 45 0010 1101 255 1111 1111

In this state all values are integers and positive only. Next consider fixed-point binary numbers in which there is a fixed binary-point separating the integer byte(s) from the fraction bytes(s). That is:

Decimal Form Binary Form

integer point fraction 45 00101101 e . 00000000 45.5 0010 1101 œ . 10000000 45.75 00101101 e — 11000000 45.875 00101101 œ 11100000

Note that in a-fixed-point number the first bit after the binary-point represents

Figure 1. Decimal Normalized Exponent Mantissa + /- E AEI1 E + 40 AE2 E + 4 .AE0 4 4 -40.0 .AE2 4 : -123.456 .123456E3 123456 -

reader is urged to try further examples. (Perhaps with a friend marking the results.)

Binary Format

As the 8& ROM program deals with binary-floating-point numbers and not decimal-floating-point numbers, the reader

the value .5 and the second bit .25 etc. (The values diminish by a factor of 2.) However, it is also possible to consider the fraction part byte by byte, which in decimal can be illustrated as follows: From above, .11100000 gives 224/256 as the fraction part and this does give 0.875. Now at last the binary numbers can be

SYNC Magazine

Conclusions Floating-point notation is logical, tedious perhaps, but very useful.

Whereas Program 1 borrows the result of the ROM program to get to its answer,

Program 2, A Floating-point Builder, ‘normalized.’ All that needs to be done is

for the whole number to be moved to the

Fi 2. left, or the right, as needed so that the ~ ١ most significant bit comes to be the first 1/2 dec. gives Exp.O Mantissa 128000 bit of the fraction part. The exponent is but 5 dec. gives Exp. -1 Mantissa 255 255 255 255

then given as the number of moves made (+ right, - left) and the mantissa is the number of bits wanted from the fraction

part.

Hence from above: Decimal Exponent Mantissa Form 45 t6 (dec.) 10110100 45.875 +6 (dec.) 10110111

(a bit 15 lost)

Note that in the example with a mantissa being limited to just 8 bits that the values 45.75 and 45.875 cannot be distinguished. This shows why the SK ROM uses not one but 4 bytes for the mantissa and even then it ‘rounds’ off values—sometimes incon- veniently.

But how are negative numbers dealt with? Well, it is easy; there is just a statement made to say whether the value is positive or negative. For example:

Decimal Exponent Mantissa +/-

Form 255 +8 (dec.) 11111111 -} -255 +8 (dec.) 11111111 -

Now it is time to run Program 1. This Floating-point Demonstration Program asks the user to enter any decimal number that he may wish, including fraction parts and ‘E's’. The program then returns the true exponent, e', and the four bytes of the mantissa. ( e’ is the exponent as developed above.) For example, entering the number

255 gives:

Decimal number 235

Its exponent 8

And mantissa 255 0 0 O0 6 And it is POSITIVE

and entering -9.9E37 will give:

Decimal number -9.9E +37

Its exponent 127

And mantissa 148 245 105 108 And it is NEGATIVE

Note: The last value can be checked by trying the line: PRINT (148/256-- 245/256**2 4- 105/25 6**3 + 180/256**4)*2**126*2 which gives 9.9E+37 as expected. (Note that 2**126*2 is used to prevent overflow.) Program 1 works by reading the floating- point number that has been attributed to the variable A as that number occurs in the variable area of the RAM. Certain changes have to be made to these bytes in order to give the true exponent and the appropriate mantissa. Note for interest the differences between values of A that ought to be the same. See Figure 2. The later result is a ‘rounding’ error.

January/February 1982

develops the result by successive multipli- cations, divisions, and subtractions. So try Program 2in order to become more familiar with binary floating-point numbers. Note: The lines 170, 180, and 210 are all attempts to get around the problem of ‘rounding’ errors. However, the serious reader might be interested in the fact that with an initial value of A such as 8 then the value of A at line 170 is: 999999999 < A = 1 ‘PRINT A’ gives 1, but ‘IF A=1’ is false. The explanation lies in the fact that A has the binary value of: EXP. 0 , Mantissa 127 255 255 253 instead of the expected EXP. 1, Mantissa 128 0 0 0 and therefore shows that the COMPARI- SON operation is of greater sensitivity than the PRINT operation. Does this ‘bug’ account for some pro- gramming problems?

Sinclair floating-point conventions

So far in this article I have described the use of the true exponent and the true mantissa, but in Sinclair machines the floating-point numbers follow two conven- tions which are:

1) The exponent byte always has 128 decimal, Hex.80, added to it, unless it is the exponent for the value zero when the exponent is always zero. Hence the 'aug- mented exponent, e, is the ‘true exponent,’ e', +128. (See how in line 120 of Program 1 this is taken into account.)

2) The true numeric bit 7 of the first byte of the mantissa which is always set in a floating-point that has been ‘normalized’ is understood to be present and the bit replaced by a sign-bit. This bit is set for negative numbers and reset for positive numbers (and zero). (See how in line 140 of Program 1 this is taken into account.)

To make this clear consider the examples in Figure 3.

Figure 3. Decimal Format True Format Sinclair Format Exp. Mant. Exp. Mant. 1.0 1 128000 129 0000 2.0 2 128000 130 0000 -2.0 2 128000 130128000 3.0 2 192000 130 64000 -3.0 2 192000 130192000 0.0 0 0000 0 0000

By way of lighter relief this month's game is an example of Basic programming that shows how bytes can be saved in 8K ROM programs— who said the 8K ROM wastes bytes?

The idea of the game is simply to find a number that results in the pattern filling the whole board. My best score so far is about 100.

Remember that RND generates a given series of numbers, depending on the SEED for its starting point, but additional dummy calls to RND will create new series. E.g., 145 POKE 0,RND would be economic for a simple arithmetic series — alternate calls to RND are used by the ‘pattern.’

Part 2of "Understanding Floating-point Arithmetic" will discuss the third language of the 8K ROM-the Calculator Lan- guage.

Bibliography

Sinclair ZX81 ROM Disassembly, Part A: 0000 H-00F54 H, by Dr. Ian Logan. Melbourne House outlets— £7. (Deals with the ‘operating system’ part of the 8K ROM program).

Sinclair ZX81 ROM Disassembly, Part B: 0F55 H-IDFE H, by Dr. Ian Logan and Dr. Frank O'Hara. Melbourne House outlets — £8. (Deals with ‘expression eval- uation' and the 'calculator routines' in full detail). a"

ZX80 ROM SWITCH (and Keyboard Beeper, and LOAD Processor)

Now you can use your 4K or 8K software at the flick of a switch!

With options, the basic unit becomes all- in-one, a Rom Switch with ZX-80 auto- reset, a Keyboard Beeper, and a Cassette- Load Processor.

The Processor lets you load with any tape output from 1 to 7 volts—automa-

tically. Iteven lets you hear the program as you load!

Everything fits inside your ZX80, for con- venience and simplicity.

Basic Switch Kit: $24.95 Assembled, Warranted: $30.95

Full-Featured Kit: $34.95 Assembled, Warranted: $49.95

To order, send check or M.O. to: Marex Electronics

2805 Abbeyville Rd.

Valley City, OH 44280

31

8K ROM 1K RAM

9 Program 1: Floating-point Demonstration Program [. .— 1 — Linear © IS PRINT AT £74 ENTER HAY. 256 Reoressio MBER 5 4 U Any decimal number r 1 n

INPUT A

3e CLS Bini LET V=sPEEK 16400+4256 ¥8¥PEEK 1 del Ws present value of Jon T. Passler = ARS. Sø CPIM BS} For the 5 bytes. TP a 60 FOR C-1 TO Get each byte from the The "Linear Regression" Program com- 2 = L i f . " . oe HERUM -PEEK (usc) e putes the linear relationship between two ,98 PRINT “DECIMAL NUMBER: TAB sets of variables, expressed as the linear 100 PRINT regression equation, and calculates the [M EU “ITS EXPONUNT"; TAB 17 coefficient of determination, an indicator i4 d ا‎ ee Form the true exponent, of the strength of the relationship. Given a 14@ PRINT “ANO MaNTISSR";TRB 17 set of two variables labelled X and Y, the رق د > قار‎ + ) 8 2 2( + 128 + ) 5 (2) > 1281 ( TA Form the true mantissa. . . . igs B 21; 5153 TAB 2525 C4): TAB 29;515 program will yield an equation describing Y as a function of X.

' 150 PRINT a op | 160 PRINT “AND IT IS"; TRE J. Give the sign. These variables can be taken from any

OSITIUE" AND (A>=8): “NEGATIVE™ A . Su i z h kg oSI tA <O: situation in which a logical relationship is

178 RUN expected, such as rainfall and crop yield, the prime interest rate and auto sales, or

time and any variable which changes

يبي يبي يبي بي يي يي يي يي ب ص ص ص

Program 2: Floating-point Builder اح‎ (generally in one direction) over a period of time. For a time series, X can be expressed iS e e Any decimal value. in periods, starting with period 1. 30 LET 5ه‎ -5 0 PERIE E T 9 ا‎ 28 oe "BECIMRL NUMBER: TAB eep the sig The coefficient of determination, R2 or 17: R squared, is a measure of how much of pe بع‎ | ti ian. 5 eg. . * . üi " Bs Se O e nM the variability in Y is "explained" by, or 76 PRINT dis P 25 LET Ea 1 un — related to, the variability in X. R2 varies هو‎ PRINT “ITS EXPONENT“; TAB 17 between 0 and 1, and R2 multiplied by 100 = 5 5 5 . . 4° “eae IF A>=.5 AND AY=1 OR A= TH Exit when “normalized.” gives a percent indication of the validity EN SOTE C En of, or accuracy in, expressing Y as a function 110 LET EzE-(a:1)-&tP0:1) Exponent changes by one. , uracy 1n, exp 8 u 120 LET B-REx€i.5r1.—55* د 13 > جع‎ A chanes by .5 or 2 fold. of X 138 PRINT AT 3,17;E Watch it changing in SLOW. ° : 148 COTO 100 For a quick example, let Y = 1 + 2* X. 150 PRIM » 180 PRINT "AND HANTISSA"; TAB 17 If X = 1, 2, and 3, then Y would be 3, 5,

“4g IF @>.9999969999 THEN LET A= and 7. Run the program, enter a 3 in

io See text. r n ntes. th 150 LET F-.003905z2498997 A little under 1/256. 6500156 to the umber of entries, then 190 FOR G=i TO 4 . Each mantissa byte. enter X's and Y's pairwise, or, to mix things ZAR LET H-INT (ALF) e decimal value. . 210 IF H»255 THEN LET H-128 Fora rounding error. up a bit, enter 2, 5, 3, 7 and 1, 3. You 220 PRINT Hi“ " e byte and a "space." : سے‎ * 230 LET A=A-INT (ASR? عد‎ Decrease A. should get the equation X g 1 T 2*X 240 LET F-F.2565 Change for each byte. back, and an R2 of 1, or 100%, since the زعم‎ L4 T is . . . . Sus P RINT equation perfectly describes the relationship 27 i 250 PRINT “AND IT IS";THB 17;"P Fetch the sign. between each pair of entries. SX ue =e HESA BINE 15 «e Linear regression can be used to approx- * 296 RUN imate the value of one variable (given the

value of another), identify the trend in time series and forecast future values, or evaluate the influence of one variable on another (R2). "s

Program 3: Floating-point Number Game

io PRINT AT URL “Se .NOT PI; “N EW NUMBER?" Jon T. Passler, 344 Cabot St., Beverly, MA 01915.

4@ CLS 50 FOR A=NOT PI IO UAL - 10 REM LINEAR REG em 6@ PRINT " ; y 20 PRINT “N OF ITEMS? AND (NOT A O AzURL "15"),;THB VA 22 IM 8 ~ gà NEXT A so CET Rec gg LET 22 "7" dx 100 LET C=NOT PI 90 PRINT “INPUT كمع‎ AND Y/S" 138 LET Bzb-SGN PI 110 IF 26م‎ THEN SCROLL 130 IF D-NOT PI THEN RU $ed لا‎ Mou au pr" LET E-INT (RND#INT Pd? -SGN 140 INPUT = : 150 LET F= INT (RND£INT PI? -SGN 16@ LET Sx=Sx+x 160 PRINT AT R4E,B* 150 LET XNEXX+AHGSS KEES 158 IF PEER (PEER URL "16398"4U 209 PEL Sl LM (rtm AL "256" #PEEK URL “163599") <>NOT $20 NEXT A PI THEN GOTO URL "120" S20 CLS m 250 PRINT 132 BRINE at UR Fae T BER PREN Y m co COUNTS TARS PERI pe fee ilis d M ad SY) /tNxXX-RBS 52 27 ae XU 218 LET A=A+tE 250 POINT s ' 226 LET B=B+F xSY / t CNEXX- "e 230 GOTO URL "110" -ABS SYxs2)s*.5))s*2

32 SYNC Magazine

8K ROM IK RAM

Lunar Lander

Chuck Dawson

You are the Command Pilot of the Lunar Lander SYNC. You are now in the fina! stages of your descent and you must make your landing before your fuel runs out. You select the thrust settings from your keyboard control system by pressing a key from 1 to 10. The computer does not wait for you to think because the law of gravity operates and the lander continues its descent. If you hit the surface at a velocity of more than 100 feet per second, you will collapse your landing gear and crash on the desolate, rock strewn surface. Once a thrust setting is chosen, it stays set until you choose another. You can cut the engines altogether by pressing zero. The engines also stop when you run out of fuel. Naturally, this is also a crash landing. When setting the power, hold down the key for a full cycle (one blink to the next) so that you are sure your key has been read by step 11.

In this game the screen display shows the rugged lunar surface at the bottom. Your instrument panel is on the right. You have vertical velocity, altitude, and fuel remaining. The 1K program just barely fits into the 1K with no room to spare. Use

Chuck Dawson, 6520 Victoria, Ft. Worth, TX 76118.

Duzzie answers

A Rectangular Problem: The answer is 51 rectangles.

Who's Who: Tom is married to Nancy, Joe is married to Mary, and Fred is married to Patty. Hint: Nancy played with Fred against her husband.

January/February 1982

the one and two digit line numbers as shown, and do not add any remarks. If you have more memory, you can finish out the surface to the right edge of the display. The 2K program adds possibilities.

If you want to change the level of difficulty, change the V in line 39. The program takes advantage of the ZX81’s INKEYS feature for game input. Be sure to enter the spaces in the PRINT statements in both versions very carefully. You can refer to the lines above and below for the spaces. The listings are a direct printout from the ZX81 and show the screen as it should look.

Two or more can play Lunar Lander with the winner being the player with the most fuel left. A crash is disqualifying, of course.

Goahead, you're GO FOR LANDING. Notes:

IK Version:

20 Graphics: Inverse O; T,6, Y; 5,6,8; R, 140, I, B.

37 Graphics: 9 graphic A, alternated with 8 graphic D.

2K Version:

29 Graphics: same as 1K line 20.

37 Graphics: 14 graphic A, alternated with

13 graphic D. E

The “26” Puzzle: (3) (1) —_——{_1.2 D—_—_—_—_—_—{ 11 )— 2)

PX (8) ED TP ERU (9)

A Word Square Problem: NESTLES ENTRANT STRANGE TRAITOR LANTERN ENGORGE STERNER

— Program 1: Lunar Lander: 8K ROM; 1K RAM _

LET H-1509

" THEN LET RsUum

F THEN LET A=@ LET U= =U+10 xRa-32

5 IF cd 58 THEN LET he T LET =INT (H-i00-4. LET Fa F-1800xH IF F «O0 THEN LET F=@

CLS PRINT RT 15-L.L:" BM": TAB L gee STAB LSU Pæ TAB LS

F A THEN PRINT TAB L:" =" BR

INT AT 12.15; “UEL RLT F

r

f) fO fU fU TI) شم‎ es post re fa A m

ip OG e ل 1 ل‎ ZZ HS D ضر زرا آنا ل‎ H "nA pa e

"e

a

E TE

n JI GI car ed se

PRINT TAB 14;U; TAB 29:H; TRE F

IF NOT H AND VUJ:-1250 THEN PR

POKE 16437.

+ Fi Ee edu

LET 10 GOTO 11 IF INKEY gî ¢ 5 THEN LET A=UR ا‎ INKEY & 1

3 IF NOT F THEN. LET nce

15 IF رن‎ THEN GOSUB ri

16 IF U«-215 THEN LET دعلا‎ 215

17 LET H=H+V)

13 IF H«50 THEN LET H=8 E C zL

(H^1004.95)

25 IF F<@ THEN LET r-e

27 PRINT AT 15-C.C«2:" “TAB C ^ 29 PRINT AT i15-L,L;" | "TH BR L; LE ae. i TAB حا‎ at S m ta - TA

P uL 9 R 3e ir ms THEN. ;BRINT TAB L«2;"x

31 NT AT .25; “THROTTLE - "GR

33 PRINT AT 12.15: “UEL. RET FUEL"

SS PRINT TRE 14:U;" "J TAB 20; Hc : TAB 2E:F: - 0

"3? PRINT, RIO 29.9: INT “#*#CRASH##" 42 IF H THEN GOTO 11

e PRINT AT Lara: OLI “UTR $2 : TARE i 2 RETURN:

Sample Run

The Flock of Geese: The number of the flock was 36. For, taking the lowest number (4), which is divisible by 2 and by 4 (as, from the conditions of the problem, it is clear that the required number must be), and going through the process suggested with such number, we have the following result: 4+4(as many more) +2(half as many more) + 1(one-fourth as many more) —11. Dividing 99(the total to be obtained after going through the same process with the actual number in the flock) by the number thus obtained, we find the quotient to be 9. 4, therefore, multiplied by 9 (—36) should be the required number. Putting it to the test, we find that 36+36+18+9=99, exactly answering the conditions.

33

Battleship was a game we used to play as kids (and later) — with pencil and paper before the toy manufacturers plasticized it. You remember— each of you placed some number of "ships" of various sizes in a coordinate grid “ocean” and then took "shots" at each other by calling out coordi- nate locations in turn. After each "salvo," hits were reported and recorded. Loss of a certain one of your ships would penalize you, Say, two shots off the next salvo. The object was to wipe out your opponent before he got you.

This Battleship Solitaire program allows you to play a similar game against the computer, but with the modification that you do all the shooting. Even though you have no ships to be sunk, you are still subject to penalties. Each time you fail to score at least one hit per salvo you lose one shot. The object of this game is to sink all enemy ships before you are out of shots.

As listed, the Battleship Solitaire program provides a 10 by 10 ocean with numerical coordinates. The “tens” digit appears on the vertical axis with the “units” digit on the horizontal axis. You will be seeking four ships of four boxes or segments each. They may be placed horizontally, vertically, or on either diagonal. Since both the bow of the ship and its orientation are determined by the ZX80 on a random basis, a new situation is added to the game: ships may abut, cross, or even share the same coordi- nate location! (What do you want from a IK program?) If the concept of intersecting battleships offends you, let some be sub- marines at different depths on the same X- Y coordinate.

Bob Dusenberry, 77 Moraine Rd., Morris Plains, NJ 07950.

34

3 E: H à Ei 3

sss

i

The program has three distinct phases. First, the four ships are randomly — and secretly — placed in the ocean. Second is

your turn. You are advised of the number

of shots per salvo (initially 5), which you take using coordinate designations. At the end of each salvo the ZX80 reports the accumulated number of "hits" on each of the four ships: A, B, C, and D. It also

1 £ 3

دس مسد لجوج ا ومو E‏ — ons‏

E

E]

EE: — — — M

displays the number of remaining shots for your next salvo, taking into account your hits and misses. Eventually it will announce “YOU WIN" or “YOU LOSE”. During the third phase of the program, accessible on a GO TO basis after the battle is over, the ZX80 generates a display of the ocean complete with those elusive ships.

Figure 1. Mapping your shots.

Numerical values keep track of

salvos.

A shot here

would be “58”.

Map shows four complete salvos. Corresponding display is:

SYNC Magazine

[ : F

= : 3

—— اس‎ E E dE 1 0

1

Before running the program it is recom- mended that pencil and paper be available for you to record your shots and hits. By drawing a 10 by 10 grid plus a separate set of four-box diagrams, one for each ship, you can keep track of shots you have taken and ships you have hit. Big hint: mark your shots and hits of the first salvo using l's, the second salvo using 2's, etc. Figure 1 shows such a diagram as it might appear part way through a game.

Start in the usual way, pressing RUN and NEWLINE. After the computer deploys the ships, unseen by you, it will display:

5 SHOTS

FIRE 1 You respond by pressing a two digit number, YX, representing your chosen coordinate. (Y is the vertical coordinate, X is the horizontal.) Follow with NEWLINE. The display now shows:

5 SHOTS

FIRE 2

Continue firing the rest of the salvo in the same manner. After you "Fire 5" the display will show, say:

HITS:

Note that ship C has been hit, as an example, and thus the next salvo is allowed to continue with 5 shots. If all ships had come up “0”, the display would show:

HTa:

You have a one-shot penalty for your failure to hit anything on the first salvo. “Four” is now the maximum number of shots per salvo during this game.

Remember that the number of hits displayed is accumulative. Thus “C:4” would indicate that ship C has been sunk. If you should hit a coordinate shared by two overlapping ships, both ships will be scored as “hit”.

The game continues, with the number of hits increasing (hopefully) and the number of shots decreasing (woefully) until the display shows:

HITS:

A:4

B:4 C:4 D:4 YOU WIN January/February 1982

Sourcebook of Ideas

Many mathematics ideas can be better illustrated with a computer than with a text book.

j

Í v ur

M

JN

A 2 p

NAM

Consider Baseball cards. If there are 50 cards in a set, how many packs of bubble gum must be purchased to obtain a complete set of players? Many students will guess over 1 million packs yeton average it's only 329.

The formula to solve this problem is not easy. The computer simulation is. Yet you as a teacher probably don't have time to devise programs to illustrate concepts like this.

Between grades 1 and. 12 there are 142 mathematical concepts in which the com- puter can play an important role. Things like arithmetic practice, X-Y coordinates, proving geometic theorems, probability, compounding and computation of pi by inscribed polygons.

Endorsed by NCTM

The National Council of Teachers of Mathematics has strongly endorsed the use of computers in the classroom. Unfortunately most textbooks have not yet responded to this endorsement and do not include pro- grams or computer teaching techniques. You probably don't have the time to develop all these ideas either. What to do?

For the past six years, Creative Computing magazine has been running two or three articles per issue written by math teachers. These are classroom proven, tested ideas complete with flowcharts, programs and sample runs.

Teachers have been ordering back issues with those applications for years. However,

many of these issues are now sold out or in very short supply.

50 we took the most popular 134 articles and applications and reprinted them in a giant 224-page book called Computers in Mathematics: A Sourcebook of Ideas.

Ready-to-use-material

This book contains pragmatic, ready to use, classroom tested ideas on everything from simply binary counting to advanced techniques like multiple regression analysis and differential equations.

The book includes many activities that dont require a computer. And if you're considering expanding your computer facilities, you'll find a section on how to select a computer complete with an invalu- able microcomputer comparison chart.

Another section presents over 250 problems, puzzles, and programming ideas, more than are found in most "problem collec- tion" books.

Computers in Mathematics: A Sourcebook of Ideas is edited by David Ahl, one of the pioneers in computer education and the founder of Creative Computing.

The book is not cheap. It costs $15.95. However if you were to order just half of the back issues from which articles were drawn, they would cost you over $30.

Satisfaction Guaranteed

If you are teaching mathematics in any grade between 1 and 12, we're convinced youll find this book of tremendous value. If, after receiving it and using it for 30 days you do not agree, you may return it fora full refund plus your return postage.

To order, send $15.95* plus $1.00 postage and handling to Creative Computing, Dept. Z0122, One Park Avenue, Room 458, New York, N.Y. 10016. Orders may also be charged to your Visa, MasterCard or American Express account—by mail include credit card name, number, and expiratioin date, or if you prefer, use our 24 hour toll free number, 800-345- 8112. In PA only 800-662-2444. Institutional purchase orders should include an additional $1.00 billing fee.

creative corpatirg

*Residents of CA, CO, DC, FL, IL, MA, MI, MO, NJ, NY State, OH, SC, TN, and VT, all applicable sales tax.

35

On the other hand, if you run out of shots first, it will show, say: HITS:

YOU LOSE The program run can be halted at any time before the end by entering “100” in place of a coordinate.

. Figure 2. Typical ship deployment displays. _—

0123456789

X XXX

P4 P4 مم‎ PS

X X X X X X X

OWOANINUIE" WHE! O

X 0123456789

NO DAIANAWNEWNE O P4 P4 P4 PS

If, now that the game is over, you are curious about the ship deployment, press NEWLINE, GO TO 700, and NEWLINE to obtain a display of the ocean and the ship deployment. Be patient, it takes something over a half minute to perform this function. Figure 2 shows typical deploy- ment displays.

Should you want to change the degree of difficulty of the game, the easiest way is to alter the initial number of shots per salvo. Fewer shots make it harder, more shots make it easier. Five shots, as pro- grammed, seem about right, and one shot, more or less, will significantly change the difficulty. To make the change, simply edit line 300 of the program:

300 LET N=5 to include the desired value of N.

Other parameter variations were tried, such as the number of ships and ships of different sizes (e.g., five ships of 1, 2, 3, 4, and 5 segments). But in the end we returned to the four ships of four segments each.

It should be pointed out that, smart as it is, the program cannot tell if you shoot the same coordinate more than once. You are not supposed to do this, but if you happen to and score another hit on a coordinante, you will get credit for an extra "hit." That could lead to a false “WIN.” Not to worry — no self-respecting solitaire player would cheat in this manner.

36

Figure 3. Battleship Solitaire Listing

DIM B(16)

LET P =1

FOR J = 1 TO h

LET D = RND(l)

LET X = RND( 7)

IF D = با‎ THEN LET X = RND(17) LET Y = RND(7)

IF D = 2 THEN LET Y = RND(19) IF D = 1 TYEN LET Y = Y + 3 TET W=1

IF D = lı THEN LET W = 7 LET 2 1

IF D = 2 T'ENIETZ 2 d

IF D = 1 THEN IET Z = -1 LET K = 9

FOR I = P TO م‎ + 3

LET B(I) =(Y+K%*2Z) * 17 +X +K * 1 LET K=K + 3

NEXT I

IT PSP + ب‎

NEXT J

LETN 25

LETC =

LET D = gf

LET E = 7

LET F = 7

LET G = 3

FOR J = 1 TO N

PRINT N; " SHOTS"

PRINT "FIRE و"‎ J

INPUT A

IF A = 19% THEN STOP

CLS

FOR I = 1 TO 16

IF NOT A + 11 = R(I) THEN GO TO 60 IF 145 THEN IETC =C + 1

IF I>) AND I9 THEN IET D 5 De 1 IF I)8 AND 12413 THEN LET E > E + 1 IF Ij12 THEN IET F 2 F + 1

LET G =1

PRINT "HITS:"

PRINT "A:'; C

PRINT "B:"; D

PRINT "C:"; E

PRINT "D:"; F

IF C)3 AND D)3 AND E23 AND Fy3 THEN

GO TO 640 LETN=N-1+G

IF N = d THEN GO TO 660 GO TO 33

PRINT, "YOU WIN" STOP

PRINT, "YOU LOSE" STOP

PRINT " 9123156789" FOR K = 1 TO 17 PRINT K - 1;

FOR L = 1 TO 17 TET AË =n" nt

FOR I = 1 TO 16

IF B(I) = 1d + K + L THEN LET AS = "y" NEXT I

PRINT A$;

NEXT L

PRINT ""

NEXT K

Four-ship array.

Preset array index.

Deploy ships, per ship

Random orientation.

70,80 Random X 1oc., modify for vertical ship.

90-100 Random Y loc., modify for horizontal ship.

Shift Y if ship slants up.

120,130 Set horiz. increment factor.

140-160 Set vert. increment factor.

Preset segment index. Deploy ship, per segment, Form coords; load array. Increment segment index.

Increment array index.

Preset no. of shots per salvo. 310-340 Preset ship hits.

Preset salvo hits. Salvo firing, per shot. 347,350 Print salvo info.

Display; input shot coords. Optional run halt.

Hit check, per segment.

Skip ship hits on miss,

20-50 Increment ship hits as req'd.

Increment salvo hit.

475-570 Print salvo results.

All ships sunk, skip to end.

Modify no. of shots per salvo. Out of shots, skip to end. Recycle if not end.

640-670 Print outcome & stop.

Print X coord. heading.

Form display, per Y coord. Print T coord.

Form display, per X coord. Preset character to blank. Scan ship array, per segment. Set char. to X if coord match.

Print character.

Terminate line. Display after last K,

SYNC Magazine

4K(8K) ROM 1K RAM

The ZX80 as a Cipher Machine

James John Hollandsworth

Would you believe that you can turn your ZX80 into a code machine? It can translate messages into gibberish that would take an expert hours to solve, yet a fellow ZX80 user could translate back into English in a few seconds.

You can do this by using the Vigenere cipher. This is probably the most famous cipher of all time, and is named for Blaise de Vigenere, the Frenchman who first described it in 1586. According to legend, he called it /e chiffre indechiffrable, the indecipherable cipher. By this he meant that if a secret message using this method of encoding fell into unfriendly hands, it would be impossible for the enemy to break it. Although today it can be broken, the process is hard, long, and tedious. It can be done only by experts in cryptology who have long messages to work with. Such personalites as Lewis Carroll and Sir Admiral Francis Beaufort were interested in this cipher. The Confederate Army used it extensively. Although the military does not use the cipher today, it remains the basis of some ciphers.

The Vigenere cipher was one of the first polyalphabetic ciphers, as opposed to monoalphabetic ciphers used since the time of Caesar. In a monoalphabetic cipher, each letter in the message is replaced by a unique letter in the cipher; e.g., A may stand for F, D may stand for R, and so on. In a polyalphabetic cipher, any letter may replace the message letter. This makes any attempt to break the cipher very dif- ficult.

James John Hollandsworth, Box 1623, Montcoal, WV 25135.

January/February 1982

Figure 1. The Vigenere Tableau

Plain-text letter

JKLMNOPQ

Key letter

N«x€c«cc-A4w»o0vozZ-x.-IOom-4mcoowv»|» »N-«x£ecc-o20v0zSrm-xc.-IOmmooo|o WPN<xKECCHHDOVOZSrAL-~ TO AMI! o OWDPN<KE<CHHnDOVOZSR-AL- TO NM! O ا عدع 5 2 و د مم بي بدح ب ع عر > بم جر وا هه‎ ION | م‎ ادوج كرح 5 2 ه م 60م م بدح > ع ير > بر حر و هه مر‎ 5 اج سس ءبع 5 2 ه م 0 م بدح > 2 ير >» رمح وه حص حرمد‎ A برع 5 2 م د 60م ى دح > ع ع > بم حر و هه حراد بي‎ 2١ =X ساس باح 52 ت ه م 2:6 م بدح > ع عر > بم حر واه هرد ج32‎ — —IOm4mOoon»wNw«x€«c-omovozzrm-x. اع 5 2 ه م 06 م بدح > 5 عد > بم دراه ه 0 مد 3:0 ات‎ 29 - 50 ع5 > ه م مج م بدح به ع بعر > بم حرو ه ورم‎ rTXc-IOmmOoo»wN«x£cec-ao»o0vozs €ErTX.—-IOmmooo»mwa«x€£«cc-2omovoz 2 5 مم و بدح »ع ع عد > يمحر وه ممم 20 ات كع‎ TO ؟< عر جاه‎ © LO ممم وى بدح »ع ع عد > بم جز وو ه حرم‎ اب كد ع 5 2 و د‎ LTO مد م دح »ع 5 عه برج واه حرم‎ )vOZZrm-X.-IOmmOoo0»m-«xt£cc-aom|m mTOvOzZr-X.-IOmmooou»w-«xt£cc-o|co 0 mDO-vOzZr-x-.-IOmmOoc»w«x€£ceca|a4 -Mo0m3O0vOZZrXxX.-IOmmOoo»w«xt€cc|c ةعم يم «ح واه حارم 52:0 ؟ كاا ع 5 زه و مم ماد‎ > | > > ب عع 5 2 0 مم م ادح‎ LO عه يم <س مهرد‎ ١ = »زا > بمج واه 6 م 5:0 ات كزع 5 2 و د 6م مدن > ع‎ | x 2 > 2ز هو ود صم م بدح‎ ARAL. TONMOOWDPN< | > «x*x€«C-4om0v0zZrx.-IOmmooo»Ni!wN

N«x*x€«c-4wm-0v02Zr-x.—-IOmmooo»

Figure 2. Sample Run

KEYWORD: SYNC

CLEAR: CRASH CURSOR IS AS BRIGH T AS A BLACK HOLE

CIPHER: UPNUZ AHTKME KK YF DJGT JL YF C TJNEC FBNW

DO YOU WISH TO CONTINUE?

The basis of the Vigenere cipher is a table known as the Vigenere tableau (what else?) shown in Figure 1. Although there are several versions of the cipher, this article deals with only two. The first uses a keyword known to both the sender and receiver. In the program the prompt will ask you to INPUT KEYWORD (1-12 LETTERS). Naturally, you may change the keyword whenever and as often as you wish as long as your receiver knows the change. To demonstrate the program, let us suppose that you must for some obscure reason send this message to a fellow ZX80 user: CRASH CURSOR IS AS BRIGHT AS A BLACK HOLE. When the screen calls for the keyword, enter SYNC. The display will prompt: INPUT TEXT. On IK RAM the number of letters and spaces (no punctuation marks) you can enter without overloading the memory is about 52. Of course, you can do longer messages by breaking them up into units of fewer than 52 characters. You will then be asked: IS THIS A CLEAR OR A CIPHER? Clear is the technical term for your message. Type itin. In a few seconds the screen will appear as in Figure 2. Copy down the cipher, answer NO to get out of the program, or YES if you have some more messages. Send the message to your friend who will follow the same routine, except that he types in CIPHER when asked, and in a few seconds he will read your message.

37

1 PRINT "VIGENERE CIPHER" 2 PRINT 3 PRINT 4 DIM A(12) 5 PRINT "INPUT KEYWORD (1-12 L ETTERS)" 10 INPUT AS 11 CLS 12 LET 55-5 20 FOR Y=1 TO 12 30 LET A(Y)=CODE(AS)-38 40 LET AS=TLS (AS) 45 IF CODE(A$)=1 THEN GO TO 5 50 NEXT Y 55 PRINT "INPUT TEXT" 60 INPUT CS 61 CLS 70 LET Tei 71 PRINT "IS THIS A CLEAR OR A/f CIPHER?" n 72 INPUT Z$ 73 CLS 74 PRINT "KEYWORD: ##";E$ 75 PRINT 76 PRINT Z$;":" 77 PRINT C$ 78 PRINT 79 IF ZS="CIPHER" THEN GO TO 16 0 80 PRINT "CIPHER:" 83 LET B=CODE(C$)+A(T) 85 IF CODE(C$)=0 THEN LET B=0 90 IF B>63 THEN LET B=(B-63)+37

The other type of Vigenere cipher we will consider is based on one letter and isa variation of the autokey system, so called because the key letter changes automatically in the message. To understand this cipher better, let us manually encipher the above message. To make the cipher even harder to break, divide the message into five- letter groups (this can be done with the keyword type also): CRASH CURSO RISAS BRIGH TASAB LACKH OLE. To encipher this you must first pick a key letter both you and your receiver have agreed upon in advance. Picking S as the The other type of the Vigenere cipher we will consider is based on one letter and isa

Listing 2. Vigenere Cipher Program

Modification for Key Letter Form

DELETE Lines 4, 12, 30, 40, 45, 50. 70, 120, 200.

Make the following line changes:

5 PRINT "INPUT KEY LETTER"

20 LET Y-CODE(A$)-38

74 PRINT "KEY LETTER: ##";A$

83 LET B-CODE(C$) 4X 110 IF NOT CODE(C$)=0 THEN LET Y -B- 38 165 LET B-CODE(CS)-Y 190 IF NOT CODE(C$)-0 THEN LET Y -CODE (C$) - 38

38

Listing 1. Vigenere Cipher Program

Keyword Form (4K ROM; 1K RAM)

100 PRINT CHR$(B);

110 IF NOT B-0 THEN LET T=T+1 120 IF T>Y THEN LET T-1

130 LET C$=TL$ (C$)

140 IF NOT CODE(C$)=1 THEN GO TO 83

150 GO TO 230

160 PRINT "CLEAR:"

165 LET B-CODE(C$)-A(T)

167 IF CODE(C$)=0 THEN LET 8-0 170 IF B«38 AND B»0 THEN LET B-6 4- (38-B)

180 PRINT CHR$(B);

190 IF NOT B-0 THEN LET T=T+1 200 IF T»Y THEN LET T-1

210 LET C$=TL$ (C$)

220 IF NOT CODE(C$)=1 THEN GO TO 165

230 PRINT

235 PRINT

240 PRINT "DO YOU WISH TO CONTIN UE?"

260 INPUT W

270 CLS

280 RUN

Notes:

4 Array for character codes of keyword.

variation of the autokey system, so called because the key letter changes automatically in the message. To understand this cipher better, let us manually encipher the above message. To make the cipher even harder to break, divide the message into five- letter groups (this can be done with the keyword type also): CRASH CURSO RISAS BRIGH TASAB LACKH OLE. To encipher this you must first pick a key letter both you and your receiver have agreed upon in advance. Picking S as the key letter, we take the first letter C. Look down the plain-text column in Figure 1 to where it meets the S key letter row. At the intersection is U. This is the first letter of your message. Repeat this process with each letter and eventually you will have: ULLDK MGXPD UCUUM NEMSZ SSKKL WWYIP DOS. Since the key letter and the cipher itself changes throughout the message, it is both extremely difficult to break and extremely difficult to encipher and to decipher. However, the ZX80 removes that difficulty. Make the modi- fications in the program in Listing 1 as shown in Listing 2. The procedure on the computer is the same as for the keyword except that you will INPUT a key letter. With the changes you will have about 90 letters and spaces for one message in 1K RAM.

Now let us see how the program works. If you closely study the tableau, you will

5 Underline indicates use of word from key board if desired to save memory.

10 Keyword. 12 Saves keyword for later dis- play. 20 Loop to load keyword charac- ter codes into array. 45 Takes program out of loop for keywords of fewer than 12 letters. 70 Initializes a value used in coding/decoding routines. 72 Nature of text. 74 Displays keyword. 76 Displays, identifies text. 79 Check if coding or decoding routine is to be used. 83 Steps up letter according to value in array. 85 Checks for space in message. 90 Loops around if coded let- ter Z. 100 Prints coded letter. 110 Increments keyword letter array unless space. 120 Loops around keyword if end is reached. 130 Next letter. 140 Checks for end of text. 160 Decoding routine is essen- to tially the reverse of the 210 coding routine.

see that the key letter A row does not really change the message. The key letter B row actually moves the message letter up one — message letter A becomes cipher letter B, B becomes C, etc. The key letter C row moves the message letter up two. The message letter then is moved the number of letters the key letter is beyond A. Also notice that when you have to move a letter so that it is beyond Z, the table wraps around back to A. So to program this I made use of the ZX80’s character code functions that allow it to treat letters as numbers as the basis of the program. When the key letter is INPUTed, its character code -38 is stored in Y (see Listing 2). This gives the number a range of A—0 to Z=25. To encipher, the program takes the code of the first letter and adds it to the value of Y. If the resulting sum is greater than 63 (the character code for Z), the program wraps around, adding the value beyond 63 to 37. It then prints the character of the manipulated variable B and goes on the next letter, exchanging the present value of Y for the value of B- 38. Deciphering is accomplished in a similar manner. The program duplicates the func- tioning of the cipher table.

For further information on the Vigenere cipher and other ciphers and codes, I would suggest checking:

Codes, Ciphers, and Secret Writing by Martin Gardner (a good beginner's book).

SYNC Magazine

The Codebreakers by David Kahn (a mammoth book describing in great detail the entire history of cryptology and cryptolo-

gists). ^a And, of course, encyclopedia articles a ar eee CE on codes and ciphers provide a quick intro- 7S PRINT duction. 79 IF ZS$t&-z"CIPHER" THEN GOTO 16 m 1 60 PRINT “CIPHER: `“ 8K Version 53 LET B=CODE C8+Y The program can be converted to 8K by 55 IF CODE C$=0 THEN LET 5 - making the changes in Listing 3. However, z 20 IF B>63 THEN LET B=(B-63) +3 for 8K you will need additional memory. 180 PRINT CHRẸ B; 2" RU NOT CODE C$=0 THEN LET Y NEN “438 LET C$=C$!2 To ) Listing 3.Vigenere Cipher Program Modifications 149 IF NOT C£&-"" THEN SOTO 863 Key Letter Form (8K ROM; over 1K RAM) IER BELT E EE 4 1 PRINT "UIGENERE CIPHER" 165 LET B-COBÉ CEY e PRINT i657 IF CODE C$=-0 THEN LET 5 -© > PRINT 170 IF 6<¢S36 AND 638 THES LET B= 5 PRINT “ INPUT KEY LETTER" Sd -—0538-B)J 19 ere dr A$ 150 PRINT CHR£E E: — a 190 IF NOT CODE C= THEN j 20 LET Y=CODE A$-38 =COQODE C&-35 7 i %35 PRINT “ INPUT TEXT" 210 LET C$-Cg&t2 TO 3 560 INPUT C$ 220 IF NOT C&-"" THEN GOTO 165 061 CLS 230 PRINT 71 PRINT "IS THIS A CLEAR OR C 235 PRINT IPHERT'" 240 PRINT "DO YOU WISH TO CONTI 72 INPUT zs5 NUE?" | 73 CLS 260 INPUT لغ‎ 74 PRINT "KEY LETTER: “RË 279 CLS 75 PRINT 230 RUN

The Root of All Evil

Playing with money can get you into trouble, all right. But it can also teach you and your -children what happens inside a computer.

By sliding and flipping pennies (affluent readers can use dimes) you learn exactly how simple computer circuits work.

The first half of Computer Coin Games provides directions and diagrams for a variety of games which can be played by anyone — computer enthusiast or not. The second half of the book explains how the games relate to com- puters.

Computer Coin Games is an inexpensive, entertaining way to introduce children and adults to binary numbers, flip flops and counters. Order your copy today.

January/February 1982

To order send $3.95* plus $3.00 postage and handling to Creative Computing, Dept. Z0125, One Park Avenue, Room 458, New York, N.Y. 10016. Orders may also be charged to your Visa, MasterCard or Ameri- can Express account— by mail include credit card name, number and expiration date, or if you prefer, use our 24 hour toll-free number, 800-631-8112. In N.J. only 201-540-0445.

*Residents of CA, CO, DC, FL, IL, MA, MI,

MO, NJ, NY State, OH, SC, TN, and VT add applicable sales tax.

creative competing

Morris Plains, NJ 07950 Toll-free 800-631-8112 (In NJ 201-540-0445)

The Best Medicine

"He said he could fix it in half the time it was taking

me, so I let him try..."

Your program is finally finished. You type RUN. Your computer replies READY. It has just eaten five hours of your life. What do you do?

Try to maintain your sense of humor—reach for The Colossal Computer Cartoon Book. Laugh atthe original adventures of Edu- Man. Chuckle at cartoons by Creative Computing favorites sandy Dean, Harbaugh, Swan, and Johns. Smile sympathetically at the ways others have sug- gested to get even with the infernal machines.

The Colossal Computer Car- toon Book contains hundreds of Clever cartoons to tickle the funny bone of anyone who has ever loved or hated a computer.

To order send $4.95* plus $3.00 postage and handling to

Creative Computing, Dept. 20124, One Park Avenue, Room 458, New York, NY 10016. Orders may also be charged to your Visa, MasterCard or American Express account— by mail include credit card name, number and expira- tion date, or if you prefer, use our 24 hourtoll-free number, 800- 631-8112. In NJ only 201-540- 0445.

*Residents of CA, CO, DC, FL, IL, MA, MI,

MO, NJ, NY State, OH, SC, TN, and VT add applicable sales tax.

Greative compating

Morris Plains, NJ 07950 Toll-free 800-631-8112 (In NJ 201-540-0445)

4K ROM 2K(1K) RAM

Inverse characters, including graphic symbols can be included in program lines as either literals or string variables, resulting in improved displays and faster graphics. Titles, headings, and prompts are examples of display items that can benefit from the added emphasis of inverse printing. Full use of the ZX80 character set also requires inverse characters.

The ZX80 achieves printing by accessing a separate set of codes in the character set that is contained in the ROM. Normal characters are assigned codes from 0 to 63 and inverse characters have codes from 128 to 191. Code values from 64 to 127 and from 192 to 211 have no valid interpretation and their use with the CHR$ function will print a question mark (*?"). Codes above 212 are reserved for Basic tokens.

You can use the CHR$(n) with any valid

. code to print a character. The program statement 10 PRINT CHR$(38) will print the normal character “A”, and the line 10 PRINT CHR5$(166) will print the inverse character “ ". The first line is equiva- lent to 10 PRINT "A", which takes fewer bytes and executes faster, but, because the keyboard has no [A] key, there is no direct equivalent for the second state- ment.

The limitation is in the input, not the interpretation. If the program contained the line 10 PRINT “A”, it would be properly interpreted and the result would be an inverse “ " on the display.

Jerry Ginn, P. O. Box 30, Shawville, PA. 16873.

40

Tioga Toads

Jerry Ginn

You can construct that line by typing

NEW and entering these lines:

10 PRINT “A”

20 POKE 16428,166 RUN this and a normal “A” will appear on the screen. When you return to the listing. you will find that the first line has been altered to read:

10 PRINT “ n

This has happened because Basic pro- grams begin at location 16424. The first two bytes contain the line number; byte three holds the decimal value 244 which is the code value for PRINT; byte four has the value 1, code for a quotation mark and byte five (address 16428) has the value 38, the code for “A”. Line 20 sets this byte equal to 166 (erasing 38). Once you have RUN this, line 20 is no longer needed and can be deleted.

If you want to use the “ ”asa string variable, edit line 10. Type SHIFT/ NEWLINE and then SHIFT/8 to remove the cursor to the right of PRINT. Type SHIFT/0 to delete PRINT and then type LET A$ = and NEWLINE. Your program should now show:

10 LET A$—" :

You can also use the edit mode to relocate the line anywhere in your program by changing the line number.

The effect is even more valuable when applied to longer strings of characters. Try this:

10 PRINT “XXXXXXXXX” (9 X's) 20 POKE 16428,128 30 POKE 16429,173 40 POKE 16430,174 50 POKE 16431,185 60 POKE 16432,128 70 POKE 16433,179 80 POKE 16434,149 90 POKE 16435,177

100 POKE 16436,128

When you RUN this you will have created the line:

10 PRINT “ {HIT N/LJ "

This line now occupies 14 bytes. To achieve this result using CHR$ would require a total of 93 bytes, almost seven times as many bytes. Note that the string of characters begins and ends with an inverse space to improve readibility. Here is a prompt with emphasis!

The method shown here can be used with any valid character code but some caution is required. When POKE is used to set the value of a byte, the previous value.of that byte is lost. If that byte held code that was critical to the interpretation of the statement, then a syntax error or a crash could result. In the example above, the addresses 16427 and 16437 contain the string delimiting quotes. To replace these with any other value would cause a syntax error. Address 16438 contains the NEW- LINE character code 118 that ends line 10. To replace it would cause a crash. It is therefore necessary that you have an "X" or other dummy character or space in line 10 for each character or space that you want in the final version of the string. A crash may also occur if you POKE an invalid character code or certain Basic token codes into a program line and list the line on the screen. So stick to the values 0 through 63, and 128 through 191. The code value 1 can also cause you difficulty. Because it is the sting delimiter, it will be interpreted as the end of the string, not as the quotation mark or ditto character. The codes for the ditto that can be used within a string are 129 for inverse and 212 for normal.

SYNC Magazine

Entering all of these POKE's and addresses can be a pain in the neck so I use a short routine which provides an onscreen progress review, allows for cor- rections and checks for the end of dummy string.

1 LET AD=16440 2 PRINT “ANY DUMMY STRING”

10 IF PEEK(AD)=1 THEN LIST 2

11 INPUT C

{2 IF C<0 THEN LET AD=AD-1

13 POKE AD.ABS(C)

14 CLS

15 LET AD=AD+1

16 GO TO2

I use this routine during program entry to build any necessary inverse strings or graphic strings and then delete it from the final version. The routine displays the dummy string, and, as you enter each code. the change is made visible on the screen. If you entered the wrong code, you can correct the last character entered by entering the correct code as a negative.

When all of the codes have been entered, the display returns to the listing with the cursor at line 2 for editing. The dummy string statement can be numbered 2 through 9 as long as it is the second line of the program. PRINT statements numbered 2 through 9 will be printed on the screen, but only the second program line will be modified. This allows you to build multi-ine graphic statements and check the whole display before editing.

To construct the toad in the program that follows, use a 3 character dummy to create each of these lines:

2 PRINT “MEI” (133,6,6) 3 PRINT "BILE T" (0,128,142) 4 PRINT ‘ama’ (135,4.4)

Start with line 4, entering the codes for the bottom third of the toad. Leave line 4 where it is and enter the dummy for line 3. When it is complete, leave it in place and enter the dummy for line 2. Each line will be modified in turn and added to the top of the previous construction. Having the the entire toad on screen will help to spot errors. After all three lines are created, they can be edited to locate them at the proper location in the program by changing line number 2 to 960, 3 to 980, and 4 to 1000.

In the following program, three of these toads hop across the screen and announce their order of arrival at the finish line. When all of the toads have finished, the race results are printed on a scoreboard making lavish use of inverse characters. If you have 2K or more of RAM, the progam can be expanded to allow two players to enter their opinion as to which toad will win the race and to comment on each player's choice after the race.

January/February 1982

The 1K version runs within 6 bytes of the memory limit. Using CHRS to print all of the inverse character would require more than 400 additional bytes and would exceed the limit.

The 2K version requires just over 1400

bytes to run. leaving about 600 bytes for additional expansion such as more toads. more players. bets on the outcome or the use of machine language routines such as found in Dr. Logan's "Auto Display Chang- ing” article (SYNC 1:3). a”

RACE RESULTS

1st 2nd PLACE PLACE B C

HIT N/L FOR NEXT RACE

** 1 LET AD=164Lø

** 2 PRINT "ANY STRING"

** 19 IF PEEK(AD)-1 THEN LIST 2 ** 11 INPUT C

** 12 IF C<@ THEN LET AD-AD-1 ** 13 POKE AD,ABS(C)

** J} CLS

** 15 LET AD=AD+1

** 316 GO TO 2

* 100 DIM T(1 110 DIM 12g DIM 130 DIM 140 LET A$

15% CLS

162 LET F$="123" 18% FRINT

19% PRINT, TIOGA COUNTY" 20% PRINT, "| TOAD RACES |" 210 PRINT, ' i

230 PRINT 248 PRINT 250 PRINT "PICK YOUR TOAD...(A,B

OR C)" 260 PRINT 270 FOR N=@ TO 1 28% PPINT "PLAYER '5N41;"? "; 290 INPUT E, 300 PRINT U 310 LET T(N)-CODE(U$)-38 320 PRINT 330 NEXT N 340 PRINT

Pic F(2 R(2 A$="GET READY"

*

KK k X k OK x

363 PRIN 370 INPUT U$ CLS 2 PRINT 41% PRINT A$ h2g PRINT 130 FOR 72-0 TO 2 hÀQ PRINT 458 FOR L=1 TO 3 46 PRINT CHR$ ( (T+38)*ABS(L=2)); 470 IF P(T)-O THEN GO TO 510 480 FOR N+1 TO P(T) hog PRINT "H"; 500 NEXT N 517 GO SUB L*2Ø+94øØ

K OK Ck ok Ok ok Ok ck o k OK ok

xX k xX k *

352 PRINT "HIT N/L TO START RACE!" T

Kk Ok OK OK k x

520 NEXT L

530 PRINT

540 NEXT T

559 PRINT ,"HIT N/A"

568 INPUT U$

570 CLS

575 LET A$="Go"

589 IF F$="" THEN GO TO 706 599 LET X-RND(3)-1

69g IF P(X)=5 THEN GO TO 594 619 LET P(X)=P(X)+1

629 IF P(X)=5 THEN GO SUB 640 630 GO TO 3968

720 PRINT ,' RACE RESULTS J"

i PRINT

74 PRINT

Tog PRINT "T IST |", D 2ND]',"[ 3RD] 76@ PRINT "PLACH', "PLACE" و‎ PLACE" TTS FOR 7-0 TO 2

798 PRINT "CD" ;CHR$(R(N)+166):; "0", 790 NEXT N

380 FOR N=@ TO 1

810 PRINT

828 PRINT "PLAYER "N+!

9039 GO SUB (F(T(N))-29)*29«09g0 848 NEXT N

850 PRINT

862 PRINT "HIT N/L FOR NEXT RACE" 870 PRINT

888 INPUT U$

89% RUN

998 PRINT " IS A FINE JUDGE" 985 PRINT ,"OF TOAD FLESH." 910 RETURN

920 PRINT " JUST MISSED," 930 RETURN

9d PRINT " IS A TURKEY," 950 RETURN

960 PRINT IM

970 RETURN

988 PRINT "E"

990 RETURN 1000 PRINT HI" 1010 RETURN

NOTE: LINES MARKED ** CAN BE ERASED AFTER ALL INVERSE STRINGS AND GRAPEICS ARE CREATED. LINES MARKED * MUST BE DELETED TO RUN IN 1K

41

8K ROM 16K RAM

Since the ZX8l uses the powerful 0 microprocessor, it is a good system for which to write machine code programs. In the past months while writing many pro- grams, I have found that there is one feature lacking on the system: a machine language monitor.

A machine language monitor is a utility, provided by most computer systems, which aids in the development of machine lan- guage programs. Its basic functions are: a) to allow you to view the contents of each byte in the system's memory, and b) to allow you to change these values.

The program provided here will allow you to perform these functions. It is a visual window into the system's memory. hence the name. In addition, it is a program which illustrates the programming litany: a program should contain very few constants intermixed with its code.

Looking at the program, you will see that the first few score of lines are all assignment statements (LETs). All arbitrary constants are specified in this section of the program. All references to these values later in the program are, then, symbolic. making the code easier to read.

Another benefit of coding the program this way is the ease of modification it provides. For example, you can change the line on the screen on which the ‘window’ begins by modifying the value of the variable PRITOP (PRImary screen TOP). Most of the visual arrangement can be changed by changing the value in one or two LET statements.

David B. Ornstein, 25 Shute Path, Newton, MA 02159.

k... n 8 €" € a

2 REM QU INDOU COPYRIGHT HEURISTICS

ANY COPY

PROGRAM BRI NU ED

OR GRAN ANET READABLE , MUST INCLUDE THI COPYRIGHT NOTICE.

(C), 3I1

S SLOAN 1@ LE HEx*1L6=2282 DisP-ieca SPLITBYTE= uin INVERSE saan HEXA تا وتاج‎ - GETKEY =2482

الك ا ا ا اي له INPUT =25e2‏ PECIG=26R2‏ AP =|16514‏ UMRMLX-18‏ CLRSECzzZ7/wc‏ DECS =2300‏ CLRPMT =2 288‏ LPD-222‏ PHMTYzLPD-1‏ PRITOPz1‏ PRIBQT =S‏

SECTOP =FPRIBQT +1 SECBOT PHTvY-i SECSIZ -5S5ECBOT-Z2EC NUM -z

FLY zB حو‎ |(Pegicuc:-PRIT

f.i

CTOP241

-dse vay celiac ade LY, ae y m e

The commands for WINDOW are:

The K key (+) is used to move to the next memory location.

J- The J key (-) is used to move to the previous memory location.

The G key (GOTO) is used to move the current location to wherever you choose. The system will ask you for an address in hex.

P- The P key (PRINT) is used to list out the contents of 10 memory locations, in hex and as characters. The PRINT starts at the current location and, when done, sets the current location equal to the next location.

The D key (DISPLAY) is used to print out 5 lines of characters which are the characters in memory. from the current location on.

FLi=o "rums ولا‎ i28

Seo LET

T D ۳4 n 5 5 2 * 1 شر‎ be be mui

Qc i

R

GOSUB PblsP

GOSUB GETEEY

PRINT RT FLY.FLX: i IF Z=S THEN cora 1* e IF كرج‎ THEN LET Z-z-

GOTO Sener iz 1) #1000

i 1 1

م م لل نم A‏ م دو | فا شم شم ل ل A EIRA Gu‏

tH

E $ &

د

NEXT t

PRINT AT FLY,i;" LET Z=AD

GOSUB HEXIG PRINT HT FLY ADA, Z$; PRINT AT FLY, , UBLX; LET Zi=PEER AD Sosa HEXS

FRINT Z$

RETURN

REN HEX16

pe pa fa O RIS frau!

ago Cua o ~d‏ ا AVIA‏

V ty Cy

TU p Re pea ضع‎ pe pe e Rea

FS pe pa ve FAS)

` David B. Ornstein.. ==

4 SET af BARN. Ab 0 LE 7 [M 1 na 7 = m. ا‎ i n Stes n" E E EN PI " 3 by all til £a «d 1 a

اک

EI

gars

Q- The Q key (QUIT) is used to exit the WINDOW program. It will leave you in FAST mode. You can re-enter the program with CONTinue.

The C key (CALL) is used to call a machine language routine. Its address is specified by the current location address.

The O key (OPEN) is used to change the contents of the current location. The system will prompt you for a 2- digit hex value. The system will then increment the current location pointer. "n

Ed. — For those who do not want to do the work of entering the program, but who do want to enjoy its benefits, it can be obtained on cassette from Heuristics, 25 Shute Path, Newton, MA 02159 for $8.00.)

LET Z12zINT 2خ‎

LET Z28-Z-zi1s256

GOSUB SPLITBYTE

ET ZS-CHR$ (Z8sNUM? +CHRS )

£2 13 رض‎ C CJ r3

LEASES aS ROG MT ROOSTER Oe PI ER

zi-zze B SPLITBYT zs- S S ICHRE

RETURN

REM SPLITBRBYTE

LET Za8-iNT (Z1.;1686!

LET za- 21-351

RETURN

REM INUERSE

FOR zzi TO LEN z$ iz) OCHR $

d

fy ¢ 35mm D ل‎ ISO NG O ZY E C

0 z4

EXT Z

8 را‎ BE IR SG SLITBYT 305 S

E Y ALRT +CHR $

ST LRRD 0 for (d fO To fi fo fü e f FO P fa Pu fu Fo ore fo 3 2 P4 O PO TOTO

f € £0 FA CUID UI GL CO HO TO ZZ TOTO PO p Re S e E

26 LET Z5$-CHR$ NUM) a RETURN @ REM GETKEY S LET SRIINKEYS L w اا‎ - PRINT AT FLY.FLXx;CHRS CB; 7" GOSUB 2470 2429 IF Z5&-"7" THEN aoro 2418 2439 FOR Z=1 TO LEN C$ 2á4Q IF Z5$-C5S(Z) THEN RETURN 2452 NEXT Z 2460 QOTO 2410 24 8 IF CBsFLU4INUERT THEN GOTO 2475 LET CB=CAa+ INVERT 24890 RETURN 2430 LET CB=CB-INVERT

SYNC Magazine

(

(Z8 4NUM) * CHR

(

RETURN

REM INPUT

INPUT Z$

ai A AN

REM DEC:

LET ZS="@@e@e8" (2 TO 4-LEN Z$

- ida mo m nma fo

EVEN ES OOS ON Gah DUE Fr [3 e rS ST OE Cie m mtu

DE رج ودج‎ -NUM

FOR B-SECTOP TO SECROT+1 PRINT HT BLA”