What's Where in the Apple. A Complete Guide to the Apple Computer

275 Pages·1983·19.94 MB·English

by  William F. Luebbert

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What's Where in the
APPLE
A Complete Guide to the Apple Computer
William F. Luebbert
President, Computer Literacy Institute
Adjunct Professor of Engineering
Dartmouth College, Hanover, New Hampshire
Apple I I e Appendix
by
Phil Daley
MICRO INK
P.O. Box 6502
Chelmsford, Massachusetts 01824
Notice
Apple is a registered trademark of Apple Computer, Inc.
MICRO is a trademark of MICRO INK. .
Every effort has been made to supply complete and accurate information. However, MICRO INK assumes no responsibility for
its use, nor for infringements of patents or other rights of third parties which would result.
Copyright © by MICRO INK
P.O. Box 6502
Chelmsford, Massachusetts 01824
All rights reserved. No part of this book may be stored in a retrieval system, transmitted, or reproduced in any way, including but
not limited to photocopy, photograph, magnetic or other record, without prior agreement and written permission of the publisher.
What's Where in the Apple
A Complete Guide to the Apple Computer ISBN: 0938222-09-0
Printed in the United States of America
Printing 10 9 8 7 6 5 4
Contents
Introduction 5
Chapter 1: There's More In Your Apple II System 7
Than You May Think
Chapter II: The World of System-Specific Programming 9
Chapter Ill: PEEKing Can Be Informative 15
Chapter IV: POKEs Can Make Changes 21
Chapter V: CALLs Can Make Things Happen 26
Chapter VI: Apple Architecture I 41
Chapter VII: Apple Architecture II: 53
Addressing in the Apple II Microprocessor
Chapter VIII: Machine-Language Programs Can Live Happily 63
In a BASIC Environment
Chapter IX: Overview of Apple System 66
Memory Allocation
Chapter X: The Apple System Quick-Access Area 71
Memory Page 0 ($0000-$00FF)
Chapter XI: The Apple System Stack Page 72
Chapter XII: The Apple Keyboard Input Buffer 78
Memory Page 2 ($0200-$02FF) and the
GETLN System of Input Associated With It ,,,
Chapter XIII: The Monitor and DOS Vector Page 85
Chapter XIV: Text and Low-Resolution Graphics Display 87
Memory Pages 4-7 and 8-11
($400-$7FF and $800-$1 BFF)
Chapter XV: 'User Memory' for BASIC Programmers 93
Typically Pages 9-149 ($0800-$95FF)
But Highly Variable
Chapter XVI: High-Resolution Graphics Display 111
Memory Pages 32-63 and 64-95
($2000-$3FFF and $4000-$5FFF)
Chapter XVII: The Disk Operating System 125
=
Default Location Memory Pages 150-191
($9600-$BFFF)
Chapter XVIII: The Specialized Input/Output Memory 134
(Some of It Behaves Very Strangely and
Some Isn't There At All)
Memory Pages 192-207 ($COOO-$CFFF)
Chapter XIX: Applesoft BASIC Interpreter 145
Chapter XX: The System Monitor Location 150
Memory Pages 248-255 ($F800-$FFFF)
Index 152
Use-Type Guide 156
Atlas 157
Gazetteer 217
Appendix A: The Apple //e --A New Edition 257
Memory Pages 192-207 and 248-255
($COOO-$CFFF and $F800-$FFFF)
Includes //e Atlas and Gazetter
Author's Acknowledgements
The information in this book has been accumulated over several years from a wide diversity of sources,
including a variety of publications from Apple Computer, Inc., articles from many Apple user group
publications and from many magazines, as well as from personal investigations triggered by one or more of
these sources.
Unfortunately no record was made in the computer database at the time of original entry of the original
source of each datum. Nevertheless the following persons, either through their writings or through per
sonal contact, come to mind as particularly significant sources of information to whom I wish to extend
my special gratitude:
Darrell Aldrich Andy Hertzfeld Lou Rivas
Rick Auricchio Donald Hyde David Roe
Bob Bishop Peter Lechner Mike Rowe
C. Bongers Lee Meador Loy Spurlock
John Crossley C.K. Mesztenyi Dick Suitor
William Dougherty Mark Pump Don Worth
Andrew Eliason Lee Reynolds Steve Wozniak
Val Golding William Reynolds
I know that the moment this book goes to the printer, the names of several others who have been inad
vertently omitted but who fully deserve to be on this list of those deserving special acknowledgement, will
rise up out of my memory to weigh upon my conscience. To such worthy but unrecognized toilers in the
orchard I offer, in advance, my sincere apologies.
William F. Luebbert
Hanover, N.H.
July 1981
Special thanks go to the Kiewit Computation Center, Dartmouth College, Hanover, New Hampshire,
for assistance in producing the Atlas and Gazetteer output.
Publisher's Acknowledgements
A work of this complexity takes the dedicated labor of many individuals to bring it to completion. The
following individuals each made significant contributions, above and beyond the call of duty.
Chief Editor: Marjorie Morse provided overall management of the project through its may iterations, in
addition to performing a superb job of editing and rewriting.
Technical Editors: Ford Cavallari and Phil Daley gave guidance and worked diligently to produce
technically accurate materials.
Layout and Production: Paula Kramer was instrumental in creating an easy-to-read product.
Typesetting: Emmalyn Bentley worked many hours on the detailed technical typesetting which resulted
in the clean look of the book.
Robert M. Tripp
Chelmsford, MA
INTRODUCTION
You can get more out of your Apple - or any block of locations. Included are the major
other computer with limited resources - by system-specific hardware locations in the
familiarizing yourself with its overall hardware Apple as well as the major subroutines,
and software environment. This book helps you parameters, buffers, and code-entry points
get to know your Apple better. It provides you in the Apple system monitor, disk
with information about hardware and software operating system, Applesoft and Integer
resources that are imbedded within the Apple at BASIC interpreters.
all times, but are usually hidden froiD. users other
3. Part III, the Programmers' Gazetteer, is a
than exceptionally well-informed and experienced
detailed breakdown of all named memory
system-level programmers.
locations in the Apple II system, arranged
What's Where in the Apple also introduces, in alphabetical order by memory location
explains, and demonstrates techniques for using name. Like the main Atlas, it contains hex
this knowledge both in a BASIC language environ adecimal and decimal memory locations,
ment and in an assembly-language environment. memory location name, and the nature and
Even more importantly, it introduces the description of the use of the location(s) by
concepts of programming in a Quasi-BASIC or the Apple II system.
system-specific BASIC environment. (Quasi
This information and these techniques should
BASIC is BASIC augmented by non-BASIC Apple
help you become a better-informed and more
assembly-language firmware.) This environment
creative programmer.
requires little, if any, user-written machine code,
but makes extensive use of machine code written It is amazing how much well-informed and
and polished by the professional programmers creative programmers can get from a, micro
who put the Apple II system together. computer when they use their knowledge of the
inner workings and hidden mechanisms of the
This work is organized in three parts:
total system's hardware and software environ
1 . Part I, 'the Programmers' Guide, is a com ment. It is disheartening to see how much time
prehensive guidebooki:o the hardware and many inadequately-informed programmers waste
firmware organization and architecture of because they lack this knowledge.
the Apple II system. It also discusses con
The information and techniques presented
cepts and programming techniques you
here should be of special value when you graduate
may find useful in exploiting the inner
from simple programs to more ambitious pro
workings and hidden mechanisms of the
grams involving careful control of man-machine
Apple II system.
interaction, analog to digital or digital to analog
2. Part II, the Programmers' Atlas, is a de conversion, extensive use of computer graphics,
tailed breakdown of the inner structure and the control of external devices, database manage
organization of the Apple II system. Ar ment, sorting, or word-processing. When (and if)
ranged in memory-address sequence, it you get into real-time programming, adding your
contains specific information on each of own specialized interfaces, performing activities
over 2000 memory locations and blocks of which require the absolute maximum speed or
memory locations inside the Apple II absolute minimum memory utilization, the in
system. This information includes hex formation here becomes critical if you don't want
adecimal and decimal addresses, memory to waste time and effort wheel-spinning.
location name (if any), and a description of
function(sJ performed at each location or Some people may take a quick look at the Pro-
6 Introduction
grammers' Atlas database listings in this book and disk operating system), can be accessed via
decide that the Atlas and the system-specific pro CALLs to provide useful capabilities without
gramming techniques are tools exclusively for writing any additional code. Some of the more
systems programmers and machine-language (or powerful and deeply imbedded machine-language
assembly-language) programmers. Because these routines will require the passing of parameters to
techniques can be extremely useful to such pro and from them. This can usually be done by
grammers, this belief has just enough superficial POKEs and PEEKs.
truth in it to be a serious conceptual and practical
Usually the code you find built into the Apple
error.
system has been carefully written in machine lan
Though the Atlas does provide a great deal of guage, optimized by good programmers, and takes
information useful in machine-language program less space or less computer time than the same
ming, it still offers at least equal assistance to the function would require if programmed by the user.
BASIC programmer. BASIC programmers who are
Even in the most awkward cases, where deeply
non-machine-language programmers may want to
imbedded firmware requires the pre-setting of
take full advantage of the capabilities of the com
machine-level hardware registers, it is possible to
puter by exercising direct control over the hard
perform the set-ups without doing any assembly
ware and the machine-language firmware which is
or machine-language coding by use of the PEEKs,
normally resident in the hardware.
POKEs, and CALLs to the register SAVE and
Often you can exercise this control by using RESTORE routines built into the system
the information in higher-level language programs monitor. (There is another similar pair of
and by changing control parameters in programs SAVE/RESTORE routines also built into the Disk
that are executed by the system itself as part of its Operating System.)
normal operations. Other times it may require the
Some users may find it more esthetically
use of machine-language subprograms which are
pleasing to perform the linkage directly by using
accessed by PEEKs, POKEs, and CALLs which are
machine-language instructions such as LOA
not themselves machine language but are written
(LoaD Accumulator), LOX (LoaD X-register) or
in a higher-level language, BASIC. Even then, the
LOY (LoaD Y- register) to form a tiny machine
only machine-language programs used may be
language linkage program, load it into memory by
those already available in firmware.
means of POKEs or S.H. Lam's technique for
PEEKs, POKEs, and CALLs all refer to memory dynamically entering and exiting the system
locations which are identifiable by what they con monitor from a BASIC program. If this is your
tain or what they do. PEEK examines the contents preference, you will find that it is neither
of a specified memory location and allows you to necessary nor desirable to use an assembler for
use that content in a program. POKE changes the this process. It is easier to hand-code from the in
content of a designated memory location to some formation in the Apple Reference Manual,
specified value. It can be used to change para perhaps using the disassembler in your Apple II or
meters of the operating environment or to set up or Apple II+ (and/ or the mini-assembler in the
change pieces of program or data. A CALL transfers Apple II) to check your work.
program control to a particular memory location
Incidentally, there could hardly be an easier
back to the CALLing routine in the user's program.
and less painful way to back gently into develop
Subroutines and other pieces of code from the ing expertise for doing machine-language/
Apple's firmware (i.e., its MONITOR and BASIC assembly-language programming than by starting
interpreter - Applesoft or Integer BASIC), and out with imbedding just a few machine-language
from its quasi-firmware (i.e., the DOS 3.2 or 3.3 instructions into a predominately BASIC program.
Chapter I functions alluded to earlier, the Apple IT system
monitor (old version) contained routines that per
There's More
formed the following functions: moved blocks of
In Your Apple ll System memory from place to place, verified that one
Than You May Think block of memory contained the same contents as
another, simulated the existence within the
Apple of a 16-bit microprocessor (the 'Sweet-16'),
1.1 single-stepped a machine-language program,
The Apple System Environment - assembled a machine-language program with
mnemonic operations codes and any of several
Hardware and Firmware
kinds of machine addressing into binary code
which will run as a program on the computer, dis~
The Apple IT system environment consists of
assembled binary code back into mnemonic form,
the system hardware, plus a great deal of software
converted decimal inputs to hexadecimal display
provided by the manufacturer, which extends the
or binary internal formats or vice versa, etc.
system's capabilities. The most important parts of
this software are often called 'firmware.' (Note: Similarly, the Applesoft BASIC interpreter (or
Firmware is software that is a permanent part of any other higher-level language interpreter) is
the computer operating environment. It is always usually also a gold-mine of useful software. For
available and may be considered an extension of example, it contains software packages for imple
the system hardware, available regardless of what menting all the operations of floating-point
kind of problem the computer is attacking and arithmetic. (Floating-point arithmetic is used for
what language it is using. Software that is put into numbers which contain decimal points or scien
a ROM (Read-Only Memory) and is available tific power-of-ten notation. J
without any special setup procedures is a prime
example of firmware. J
1.2
The 'firmest' of the firmware in the Apple IT is
Making Hardware and Firmware
the system monitor. Without the monitor you
Resources Accessible · ·
could not load other programs into the system,
nor make effective use of the keyboard for input,
The Programmers' Guide provides a frame
or the display screen for text or graphic output;
work for understanding both the overall organiza
the system would be functionally inoperable.
tion and structure of the Apple system and those
However, the monitor is not the only piece of programming techniques which exploit that
firmware you'll normally find imbedded in the knowledge. The Atlas and Gazetteer provide
Apple every time you try to run a program. To use supplementary detailed reference information
the BASIC language you need a BASIC inter you need in actual programming.
preter, either Integer BASIC Ol" Applesoft BASIC.
This detailed information is presented in
To use the disk sub-system you need disk
'Geographical' (Memory Map) order in the Pro
operating system firmware, usually known as
grammers' Atlas (Part IT) with an alphabetic-by
DOS firmware.
name Programmers' Gazetteer (Part ill) to pro
These three major software/firmware vide an alternate means of retrieval. An optional
packages each contain a gold-mine of carefully diskette version of the database together with a
written routines which can make it possible to retrieval program provide machine-implemented
write better, faster-running programs. However, selective retrieval as well (see page 4).
most of these resources, and many of the
The information in both the text and on the
hardware-specific characteristics of the Apple
diskette can stand alone as sources and tech
system remain hidden away and are not readily
niques for making more effective use of the Apple
available to the typical Apple user. Oftentimes
IT. You can learn a great deal about system
even finding out about their existence and
specific programming techniques for the Apple IT
capabilities becomes a task worthy of the talents
and about its hardware/software architecture
of Sherlock Holmes. Sometimes only the manu
from the text. You can find out how particular
facturer's 'systems programmers' learn about
sections of memory are used and about the char
some of the features.
acteristics of software in particular areas of
Even within a single module of firmware there memory. You can use the Atlas database tables or
can be a great diversity of routines useful to the printouts from the diskette to identify software
average programmer. For example, in addition to by specific names. And you can search the disk
the program-loading, input/o utput, and graphics ette database using the retrieval program on the
8 Chapter I
diskette to find hardware locations, parameters, Parts II and III of this booklet. The answer is sim
or software descriptions which use keywords ple; if you already know about where in the Apple
you're interested in exploring. system a particular parameter, subroutine, or
capability should be located, it is probably worth
For example, if you're interested in all
while to go to the appropriate area of memory in
memory locations and software in the Apple that
the tabular printout (Part III) and use the diskette
relate to the 'slots' used for plug-in of auxilliary
only if you can't find what you are looking for.
cards, you could use the diskette to conduct a
(After all, the information might be somewhere
keyword search on the word 'slot'. To find out
else in the Apple where you didn't expect it.) If
about hi-res graphics you could search on the
you already know the standard Apple name for a
word 'HI-RES'. (In both cases you would be flooded
parameter or subroutine, it is probably best to
with more information than you are likely to
look it up in the alphabetic-by-name tabular
want or use, but it would all be information
printout (Part III). If you don't find it, try the
relative to your request. However, with a little
diskette - it is often more difficult to determine
practice you will learn to narrow your requests ~o standard Apple names for memory locations or
exactly the information you want.) You could, m
subroutines than to find out information about
principle, achieve the same results more labor
what they do.
iously (and with a higher human-error rate) by
scanning through the forty-odd pages of Apple In some cases the information on the database
Atlas database printout in Part II of this book. diskette may be more brief than that in the
tabular printouts. This was necessary to squeeze
The Atlas will also help you find information
the information into the available space on the
you may already have available in sources such as
diskette. A larger version of the Programmers'
your language-oriented reference manual (e.g.,
Atlas database and retrieval program is available
the Applesoft Programmers' Reference Manual)
via timeshare from the Apple information library
or a systems reference manual (e.g., the Apple
(APPLELIB * * *) on the Dartmouth College time
Reference Manual).
share computing system. This system is acces
You may want to know when you should use sible to any qualifed user from anywhere in the
the diskette database and retrieval program and nation via the communications facilities of
when you should use the tabular printouts in TELENET.
Chapter ll dependent features (such as PEEKs, POKEs, and
The World of CALLs) built into their versions of BASIC. Often
they may see interesting, but difficult-to
System-Specific Programming
understand, published programs for the Apple
which are made up almost exclusively of these
commands. These programs are often written by
2.1
highly experienced assembly-language program
BASIC Doesn't Have To Be mers who use techniques not commonly covered
A Straightjacket; in academic textbooks or computer programming
Neither Does Assembly Language courses. Many programmers get the false impres
sion that they need esoteric knowledge if they do
Often inadequately-informed programmers more than use an occasional PEEK, POKE or CALL.
feel they are boxed-in by the characteristics and
limitations of the BASIC language, not realizing
2.2
that the versions of BASIC available on the Apple
System-Specific Programming:
(and many other microcomputers) are not as
limited as they think. These versions do allow A Programming Approach for BASIC
you to access and exercise significant direct con and Assembly-Language Programmers
trol over the hardware and firmware of your
system. Programmers often mistakenly assume that to
take effective advantage of the inner workings
This work emphatically rejects the viewpoint
and hidden mechanisms of system software and
that when using BASIC you must give up control
hardware capabilities they must abandon BASIC
of what is happening in the software and hard
and become assembly-language experts. Under
ware of your computer.
these circumstances it is not surprising that they
This work also emphatically rejects the view don't feel strongly motivated to learn about
point that BASIC and assembly-language pro machine-language code - information which is
gramming are such totally separate worlds that in their computers and potentially available for
the programmer must choose one or the other, their use every time they run a BASIC program.
but never mix them in the same problem. It rejects
Assembly-language programming is not every
the viewpoint that you must become an expert
one's cup of tea. Many excellent programmers
assembly-language programmer before you can
shy away from assembly and machine-language
understand and make effective use of the inner
programming because they do not want to get
workings and hidden mechanisms of the software
bogged down with its limitations.
and hardware of your computer.
Well-written assembly-language programs do
Instead, this book adopts the viewpoint that
often run faster and use less memory than BASIC
with the Apple (and other microcomputers) you
programs, but they usually take longer to write
can readily shift back and forth along a con
and longer to test and debug than BASIC pro
tinuum of possibilities from (nearly) system
grams. Human error rates in writing assembly
independent BASIC, to system-specific BASIC, to
language are often high. Assembly-language pro
BASIC augmented by assembly or machine
grams are harder to read and understand than
language, to assembly language using BASIC
BASIC programs. And, they are even harder to
input-output and service routines, to full use of
modify and update without extremely careful
assembly language.
documentation - and most assembly-language
In fact, What's Where in the Apple suggests programs are difficult to document well. There is
that the best results are obtained by taking a also a significant investment in time and effort
careful look at the circumstances and at the involved in learning how to control the operation
nature of the problems being attacked before of an assembler and how to use it effectively.
deciding where to position yourself on this spec
Often programmers associate these limita
trum of alternatives. You'll discover new
tions not just with full-scale assembly-language
capabilities you can use in your own program
or machine-language programming efforts, but
ming which will challenge your creativity and in
with all aspects of hardware-dependent and
crease your willingness to undertake more dif
system-specific programming. As a result many
ficult and interesting programming tasks.
avoid any programming effort that seems to have
It is amazing how many capable and well any whiff of involvement with machine language
informed microcomputer users fail to appreciate or the details of their computers' internal
the full significance of system- and machine- architecture.