Assembly lines, the book : a beginner’s guide to 6502 programming on the Apple II

286 Pages·1982·8.547 MB·English

by  Wagner, Roger

ASSEMBLY LINES:
THE BOOK

ASSEMBLY LINES:
THE BOOK
A Beginner's Guide
to 6502 Programming
on the Apple II
BY ROGER WAGNER
Softalk Publishing
1982
''"·----~--------------------------
~] 1982 by Softalk Publishing Inc. All rights
reserved. No part of this publication may be
copied, transmitted, or reproduced in any way
including, but not limited to, photocopy,
photography, magnetic, or other recording,
without prior written permission of the
publisher, with the exception of program
listings, which may be entered, stored
and executed in a computer system, but
not reproduced for publication.
Library of Congress Catalog Card Number: 81-85708
Softalk Publishing
11021 Magnolia Blvd,
North Hollywood, CA 91601
Design by Kurt A Wah!ner Printed in the United States o:' America
To My Father
Table of Contents
INTRODUCTION .......................................................... ix
1 APPLE'S ARCHITECTURE . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . 1
6502 Operation. Memory Locations. Hexadecimal Notation.
2 ASSEMBLERS ........................................................ 13
General Discussion. Source Code. Object Code. Source Code Fields.
Pseudo Opcodes. Load/Store Opcodes.
3 LOOPS and COUNTERS .......................................... 23
Binary Numbers. The Status Register. Incrementing and Decrementing.
Looping with HNF. ~"
4 LOOPS, BRANCHES, COUT, and PADDLES .............. 31
Looping with BFQ. Branch Offsets and Reverse Branches. scr,2en Output
using COlJ r. Reading a Game Paddle. Transfer Commands.
5 1/0 ROUTINES using MONITOR and
KEYBOARDS .......................................................... 41 ~~""
Review of Concepts. Compare Commands and Carry Flag. Lsing
Monitor Programs for I/O Routines. Reading Data from Keyboard.
6 ADDRESSING MODES ........................................... 51
Immediate, Absolute, Zero Page, Implicit/Implied, and Relative
Addressing Modes. Indexed Addressing. Storing Pure Data.
7 SOUND GENERATION ROUTINES .......................... 61
Delays. Altering Program Length. Delay Value in Memory. Delay from
Keyboard and Paddles.
8 THE STACK ........................................................... 71
LIFO. Slack Pointer. l'l!A !'LA. Stack Storage Capacitv.
9 ADDITION and SUBTRACTION .............................. 75
Binary Numbers. AllC. Clearing the Carrv. Two-Byte Addition. SHC.
Setting Carry for Subtraction. Positive and Negative Numbers.
Ones' Complement. Twos' Complement. Sign Flag.
vi
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10 DOS and DISK ACCESS .......................................... 89
Disk Access. Overview of DOS. Diskette Organization. Modifying Access
Utilities.
11 SHIFT OPERATORS and LOGICAL
OPERATORS ......................................................... 103
Shift Operators. Logical Operators. AND. Operational vs. Processing
Modes. Flow of Control. Inverse Flag. Masking. Inclusive OR.
Exclusive UR.
12 1/0 ROUTINES ...................................................... 121
Print Routines: Data Type; Special Type. Manipulating the Stack Return
Address. Input Routines: Binary Input; Combination Applesoft/ Assembly
Language.
13 READING/WRITING FILES on DISK ....................... 129
Bl.OADIBSAVE. Name File Program using String and Singlt• Key Input,
Print, and nos Command Routines. Text Files. Ol'EN!READ,
OPEN/WRITE. Simulating Program Execution: LA'\JC, CCRLIN,
Memory Location $33.
14 SPECIAL PROGRAMMING
TECHNIQUES ....................................................... 145
Relocatable vs. Nonrelocatabk Code. JM!' Commands. Determining
Program Location. JSR Simulations. Self-Modifying Code. Indirect
Jumps.
Appendix A ................................................................. 163
Contest.
Appendix B ................................................................. 171
Assembly Language Commands: Description and Uses.
Appendix C ................................................................. 243
6502 Instruction Set.
Appendix D ................................................................. 259
Monitor Subroutines.
Appendix E ................................................................. 263
ASCII Code and 1ic'xt Screen Charts.
Index .......................................................................... 267
vii

INTRODUCTION
One often gets the impression that programming in assembly
language is some very difficult and obscure technique used only
by those advanced programmers. As it happens, assembly language
is merely different, and if you have successfully used Integer or
Applesoft Basic to do some programming, there's no reason why
you can't use assembly language to your advantage in your own
programs.
This book will take a rather unorthodox approach to explain
ing assembly programming. Because you are presumably some
what familiar with Basic, we will draw many parallels between
various assembly language techniques and their Basic counter
parts. An important factor in learning anything new is a familiar
framework in which to fit the new information. Your knowledge
of Basic will provide that framework.
[ will also try to describe initially only those technical details
of the microprocessor operations that are needed to accomplish
our immediate goals. The rest will be filled in as we move to
more involved techniques.
This book does not attempt to cover every aspect of machine
language programming. It does, however, provide the necessary
information and guidance to allow even a somewhat inexperi
enced person to learn machine language in a minimum of time.
You should find the text and examples quite readable, without
being overwhelmed by technical jargon or too much material
being presented at once.
I'd like to take this opportunity to briefly mention a few of
INTRODUCTION ix