128 machine language for beginners

418 Pages·1986·33.92 MB·English

by  Mansfield, Richard

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Appendix C, "Commodore 128 MemoryMap/' wasoriginallypublishedin COM-
PUTEl's 128Programmer's Guide, copyright 1985, COMPUTE! Publications, Inc.
Copyright 1986, COMPUTE! Publications, Inc. Allrightsreserved.
Reproduction ortranslation ofanypart ofthis work beyond thatpermittedby
Sections 107and 108 ofthe United States CopyrightAct without the permission of
the copyright owneris unlawful.
Printedin the United States ofAmerica
10 987654321
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ISBN 0-87455-033-5
Theauthorandpublisherhavemadeeveryeffortinthepreparationofthisbooktoinsure theac- . .
curacyoftheprogramsandinformation.However,theinformationandprogramsinthisbookare J [
soldwithoutwarranty,eitherexpressorimplied.NeithertheauthornorCOMPUTE!Publications, *—J
Inc.,willbeliableforanydamagescausedorallegedtobecauseddirectly,indirectly,incidentally,
orconsequentiallybytheprogramsorinformationinthisbook.
Theopinionsexpressedinthisbookaresolelythoseoftheauthorandarenotnecessarilythoseof * I
COMPUTE!Publications,Inc.
COMPUTE! Publications, Inc., PostOffice Box5406, Greensboro, NC 27403, (919) •< j
275-9809, ispartofABC ConsumerMagazines, Inc., one oftheABC Publishing l J
Companies, andisnotassociated with anymanufacturerofpersonal computers.
Commodore 128 is a trademark ofCommodore ElectronicsLimited.
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Contents
Preface v
Introduction: Why Machine Language? ix
1 How to Use This Book 1
2 The Fundamentals 9
3 The Monitor 29
4 Addressing 51
5 Arithmetic 73
6 The Instruction Set 89
7 Borrowing from BASIC 127
8 Building a Program 137
9 ML Equivalents of BASIC Commands 155
10 The 128 Environment 189
11 Built-in Routines 199
Appendices 213
A 8502 Instruction Set 215
B How to Use LADS 247
C Commodore 128 Memory Map 267
D LADS Source Code 275
E Library of Subroutines 343
F Typing In LADS 349
G Commodore ASCII Codes 379
Index 389
Disk Coupon 393
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Preface
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Few personal computers—indeed few computers of any kind—
have been as thoughtfully designed or as attractive to people
P"! who enjoy programming as the Commodore 128. It has sev
eral environments, optimized disk access, 16 memory config
urations, and dozens of special codes, escape sequences, and
screen controls. It's a generously equipped toolbox for people
who like to customize their computers and their software. And
it offers the programmer a set of tools which are hitherto un
matched in variety and power in a consumer computer.
It represents the best of a breed: the eight-bit machine.
These computers are built on chips which work with one byte
at a time—the 8502 chip in the 128 and the 6502 chip upon
which most of the first consumer computers were built. They
are a technology in its twilight, but the 128 has significant
strengths and could well survive for years as a model of what
personal computers can be.
The 68000 chip is emerging—Commodore's Amiga, Atari's
ST, and Apple's Macintosh all use it—and no one can turn
back the clock. This new 68000 is bigger, faster, and much
more flexible than eight-bit chips. It can manipulate four bytes
at a time and directly access massive amounts of memory. It
doesn't need to switch banks, and it races along at eight times
the speed of the older chips. It's the end of an age.
Nevertheless, excellence can and often does appear at the
end of an age. Bach, probably the finest musician ever, sum
marized and synergized the music of his time. He embodied
pi the best of what was then known. As it turned out, his sum
maries and synergism have proven timeless and durable.
There has been more dramatic music since, equal music per-
(jmm\ haps, but no better music. The Commodore 128 is a complex,
full, and rich summation of the best that is possible with an
eight-bit machine architecture. It is a classic programmer's
j—1 computer. You can spend years exploring its abilities.
However, the heart of a computer is only accessible via
machine language. Several years ago I decided to learn to pro-
j""! gram in machine language, the computer's own language. I
— understood BASIC fairly well and I realized that it was simply
not possible to accomplish all that I wanted to do with my
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computer using BASIC alone. BASIC is sometimes just too slow. j /
I faced the daunting (and exhilarating) prospect of learn- {—'
ing to go below the surface of my computer, of finding out
how to talk directly to a computer in its language, not the | f
imitation English of BASIC. As I was to discover, something (—■>
amazing lies beneath BASIC.
Few events in learning to use a personal computer have \ )
had more impact on me than the moment that I could in- <—'
stantly fill the TV screen with any picture I wanted because of
a machine language program I had written. I was amazed at
its speed, but more than that, I realized that anytime large
amounts of information were needed onscreen in the future—
it could be done via machine language. I had, in effect, created
a new BASIC "command" which could be added to any of my
programs. This command—using a SYS instruction to send the
computer to my custom-designed machine language routine—
allowed me to have previously impossible control over the
computer.
BASIC might be compared to a reliable, comfortable car.
It will get you where you want to go. Machine language is like
a sleek racing car—you get there with lots of time to spare.
When programming involves large amounts of data, music,
graphics, or games, speed can become the single most im
portant factor.
.After becoming accustomed to machine language, I de
cided to write an arcade game entirely without benefit of
BASIC. It was to be in machine language from start to finish. I
predicted that it would take about 20 to 30 hours. It was a
space invaders game with mother ships, rows of aliens, sound
... the works. It took closer to 80 hours, but I am probably
more proud of that program than of any other I've written. , >
After I'd finished it, I realized that the next games would —I
be easier and could be programmed more quickly. The mod
ules handling scoring, sound, screen framing, delay, and ^ »
player/enemy shapes were all written. I only had to write < /
new sound effects, change details about the scoring, create
new shapes. The essential routines were, for the most part, al- ^ *
ready written for a variety of new arcade-type games. When 1 i
creating machine language programs, you build up a collection
of reusable subroutines. For example, once you find out how ^ >
to make sounds on your 128, you change the details, but not i 1
the underlying procedures, for any new songs.
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The great majority of books about machine language as
sume a considerable familiarity with both the details of
microprocessor chips and with programming technique. This
book assumes only a working knowledge of BASIC. It was de-
signed to speak directly to the amateur programmer, the part-
time computerist. It should help you make the transition from
BASIC to machine language with relative ease.
You'll quickly discover that machine language is your key
to the excellence and power waiting within Commodore's 128.
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