Table Of Content_by Jim Sather
Foreword by Steve Wozniak
(@XS auatmry sorrware
$22.95
Understanding the Apple IT
A Learning Guide and Hardware Manual
for the Apple II Computer
Quality Software is pleased to present the definitive source of information about how the Apple works.
Jim Sather has conducted an exhaustive analysis ofthe inner workings ofthe Apple I computer. Now he
hhas documented his findings in a way that will benefit everyone interested in microcomputer technology.
About the Author
James edi Saher, aformer electronics eld technical
‘epresetative lor ITT Gillan san independent author,
Programmer, and desimer of circuits for microcomputers,
Specaliangin the Apple TL
derstanding te Apple srt the Ape a Ape Pa
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ISBN 0912985011
derstanding the Apple I
‘+ Document all motherboard rei ineluding
some discssed nowhere ee
+ Describes dik controler operation, including
previously undocumented deal ofthe loge tate
Sequence
+ Explains RAM and ROM card operation,
+ Reveals previously unnoticed features of Apple
raps
+ Contains 23 software and hardware Application
‘Notes including shit key mod, disk wnt protect
‘od; and EPROM mods,
‘+ Tncludes a chapter on maintenance that provides
Simple woubleshooting ps
Ifyou areat all curious about how the Apple I works,
youaresure to find Understanding the Apple I very
‘lute eis an deal book fora mcrocomputer
Tandamestals couse based on the ADDIE
Understanding the Apple II
by James Fielding Sather
QUALITY SOFTWARE
21601 Marilla Street
Chatsworth, California 91311
8} 204 IS
Univ.
Bibliothek
Bielefeld
Production Editor: Kathryn M. Schmidt
Original Schematies and Diagrams: James Fielding: Sather
Art Direetor and Cover Design: Vie Grenrack
Cover Art: George Garcia
Schematic Art: Ron Widman
Photography: Gainsforth Studios
Compositor: Ameriean Typesetting, Ine.
Printed By: California Offset Printers
Comgright © 1084 by Quality Soare, All rights reserved. No part ofthis book may be reprinted, or
‘reproduced or utilized in any farm or by any eletronic, mechanial, or other means, now known oF
hereafter invented, ineluding photocopying and reeording, or in any information storage and retrieval
system. without permission in writing fom che Publisher. No patent Viability isassumesd with respect to
theuse of the information contained herein, Whileevery precaution as been taken in the preparation of
this book, the publisher assumes no responsibility for errors or omissions. Neither is any liability
assumed for damages resulting from the use ofthe information contained herein,
International Standard Book Number: 0-912985-01-1
Printed in the United States of Amerion
BI 100384105+01
ONTO
Behausted after addressing an Applefest audience
in Anaheim, Twas offered a ride to the airport by a
stranger who was writinga book on something Apple
related and who wanted to talk to me, The traffic
congestion, missed exits, and airport confusion have
deeper meaning to a computer designer, but I shall
never forget the conversation we had forthe nezt ow
pleofhours. Jim Sather proceeded toexplain details,
‘anomalies, oversights, and paradores af the Apple HL
hardware as we drove the LA freeways. Designers
like myselffind itrery rewarding toenconnter others
‘oho understand and appreciate what we feel are the
trieks and magic of our eirewits, Iwas able to add to
the magic by explaining the unusual framework in
hich the computer was designed.
The Apple II was designed ax an interesting hobby
projec to “shou off" atthe local computer club. Only
‘ane or feo were intended to be built, and then for a
market of one (myself). Component selection was
biased by what wax easy to ablain ard affordable
Features such as game 1/0, color, and graphies were
‘added to impress friends with specif applications
The driving motivation was to accomplish a tot with
very few eanponents, In this framework the system
features were largely influenced by the technical
environment—whieh ICs oreupying how much board
space, the bandiwidth of normal home TVs, ete. It
mare common today to specify features based on
maarbet considerations.
foreword
Since the hardware and softioare taake were not
partitioned in advance for separate groups to work
on, a tremendows syneriy evolved. Understanding
the Apple II respects this clove interdependence, It
contains discussion and examples throughout. Hard
ware and software developers alike (and enthusiasts
‘and stuctents too) will gain greatly from this manual
This is especially true for Chapter 9 on the loopy
disk and controller, one of the last individwad eom-
puter projects and certainly my personal favorite.
‘Design considerations must be resolved in news
creatine ways when they are not commonplace,
Appreciate the challenge of striving for low eompo-
ent count yet including many features of today’s
‘personal eompucersor thefirsttimeereron lowcost
computer. These features include dynamic RADI.
video terminal appearance, plastie ease, BASIC in
ROM, color, hi-res graphies, paddles, speaker,
switehing power supply, and more. Normally, large
successful companies generate good products. This
time ithappened the other way around. The Apple IT
isa product hich generated one ofthe greatest com-
panies ever! 10% about time the stony of ite innards
‘was presented so well.
Hhoe Hood,
Vy
Dedication
On behalf of my father, Fredrick, and my brothers and sisters, Lee, Jenny, Tim, Mary, Mike,
and Joe,
to my beloved mother,
Frances Janet Nalder Sather.
Acknowledgements
Deborah A, Sather entered the original manuscript to word processor and offered numerous
suggestions that made deseriptions more clear. She also tolerated the disruption of a wageless
author cluttering up the household with his presence and demands.
ITT Gitfillan earried me on leave of absence for seven months before we mutually agreed to
terminate my employment.
"Aalto provided suggestions and corrections which improved Chapters 4and9. Don Worth
{id the same for Chapters 2 and 9.
‘The Apple IT computer is an adult toy of wonder-
ful depth which brings forth the pride and ereativ-
ity that resides inall ofus, It isa gymnasium for the
mind which tests and developsour mental agility. It
‘teaches us about itself, and there is much to learn
Learning about the Apple through creativeusage is,
tan exciting and fulfilling, if sometimes frustrating,
‘experience. The frustration comes from the diffi-
culty of the puzzles with which the Apple confronts
tus, The fulfillment eomes from learning, to manipu-
late the powerful machine,
‘The front line source of information about the
Apple is the documentation provided with the com-
puter: the Apple IT Reference Manval, the Applesoft
I BASIC Programming Reference Manual, The
Applesoft Thtorial, and The DOS Manual. Maga-
ines and other books provide a wealth of informa
tion for the inquiring user. The great self-teaching
‘experience is programming, and persons who choose
to program the Apple in any of the various lan-
‘guages quickly increase their familiarity with the
features of their computer. Another important
source of knowledge is the study of professionally
rritten programs such as thesystem monitor. listed
in the Apple II Reference Manual. Gradually, the
student acquires a working knowledge of the var-
fous hardware features ofthe Apple. This is impor~
tant, because it is the hardware features which
ultimately define the capabilities and imitations of
the machine.
"The purpose of Understancting the Apple IT is to
assist the student of the Apple in accelerating the
process of assimilating knovledge about his or her
computer. This book is hardware oriented, and,
therefore, fills a longstanding information gap in
[Apple literature, Emphasis is placed on achieving
preface
aan operational knowledge of the Apple. based on an
understanding of how the hardware works. Opera
tional knowledge consists of knowing what the
Apple can do, knowing how to make it do it, and
‘knowing what a controlling program is making the
Apple do. By way of assisting the reader in achiev-
ing his goals, the goals of this book are:
1. To provide clear descriptions of microcomputer
fundamentals and of the operational features of
the Apple.
2, To provide examples of how a knowledge of the
operational featuresof the Apple ean beapplied.
8, To provide the most thorough hardware refer-
cence material available for the benefit of tech-
nically oriented readers and for those readers
‘who wish todelvevery deeply intotheseerets of,
the Apple,
4, To serve as a text book for Apple based high
‘school or university courses teaching eomputer
fundamentals.
‘To fill information gaps in Apple literature by
describing: previously undocumented opera-
tional features.
Because of the great differences in hardware
between the Apple Ile and previous Apple Ils, no
attempt is made in this book to document the opera
tion of the Apple Ile. The hardware differences
Detween the two computersare of such consequence
that the Apple He would itself be the subject of a
‘book similar in seope to thisone.* All mention of the
Apple or Apple II in this book is meant to refer to
‘Apple Is prior to the Ie. Yet it is only prudent to
The book Cert the Ae He by Si Sather
le for release by Qual Softvare i 1284
ced:
acknowledge here that the Apple Ile is a consider~
fable improvement over the older Apple Ils. In par
tiewlar tome Apple weaknesses mentioned in this
‘book do not pertain to the Tle. This includes most
‘keyboard and text display deficiencies and incom-
patibility between motherboard ROM and equiva
lent EPROM,
Persons who will benefit from readings Under-
standingthe Apple [Tare inguiring people who want
to spend some time learning about this machine.
Generally speaking, this refers to those persons who
program the Apple in any language. Itis recognized
that different people will earry their investigation
todifferent depths. For those who have not the time
‘or desire ta reach the greater depths, the Overview.
Bus Structure, and Address Decoding chapters
(Chapters 1, 2, and 1), as well as the Application
‘Notes at theend of every chapter. arerecommended
‘as providing a good foundation for understanding
the Apple. A a textbook for students ora learning
‘guide to hard core enthusiasts, cover to cover read~
ing is recommended.
‘While an inquiring mind isthe only qualification
required of a reader of this book, certain sections.
will be difficult for those readers without some
Dackgroand knowledge. In order of descending:
importance, helpful background knowledse in-
cludes understanding of BASIC programming lan-
‘guage, hexadecimal and binary number systems,
6502 assembly language, and technical ilustrative
aids such as timing diagrams, truth tables, and
schematie diagrams, I.should be noted by all read
ters that exeept for the technical aids, they will even:
tually have to aeguire the listed background know.
‘edge if they are to achieve a real understanding of
the Apple computer. It is hoped that the nontechni-
calaids and language in Understanding theA pple IT
are sufficiently descriptive, and that a technical
background, although helpful, is not necessary. In
general, the Tater chapters contain more detailed
And technical information than the earlier chapters,
fand the earlier sections in each chapter are less
technically oriented. Appendices F and F contain
some basic information on number systems and cir-
teult symbols for those readers who come to this book.
‘with no previous knowledge of those subjects.
Even though Understanding the Apple 11 is not 8
programming instruetion manual, many program-
ming examples are given in the body of the text
‘which illustrate applications of principles being
discussed, Where possible, these examples are writ
ten in BASIC so that the clearest possible level of
illustration results, In addition, a number of Soft:
‘ware Application Notes are included at the end of
various chapters which further demonstrate the
application of principles. These programming notes
fare included because understanding the Apple
{neludes a combination of programming knowledge
and hardware knowledge. Unless noted otherwise,
all software examples are creations of the author
land are hereby placed in the public domain. The
author requests that he be given credit as the pro-
‘grammer in all reproductions of these programs.
‘A number of Hardware Application Notes are
also included at the ends of chapters. Some of these
‘Notes are hardware projects which demonstrate
relevant principles. Other Notesare simpledeserip~
tions of modifications to the Apple which enhance
operation insome way, suchas the SHIFT key modi-
fication, Figures 2.11, 8.12, 8.18, 3.15, 4.8, and 4.10
‘are all original designs of the author. Readers are
‘encouraged to study or build themor integrate them
{nto their own designs. The author requests that he
begiveneredit as thedesigner in any reproductions
or other use of these schematies. D MAnual Con
‘roller (Figure 4.8) is being manufactured by the
Southern California Research Group, and is avail-
able for purchase as noted in Chapter 4.
‘Several Hardware Application Notes detail mod-
ifieations to part of the Apple or Apple peripherals
Please read the NOTE OF CAUTION followingthe
Table of Contents before performing any modifica-
tions to your equipment. It is recommended that
‘readers unskilled in electronies workmanship who
desire a modification have the work performed at a
computer dealership or by askilled friend. Persons
‘who modify their Apples should be able, or know
someone who is willing and able, to repair the modi
fied assembly if it should fail
‘Understanding the Apple IL is the result of an
intensive investigation of the Apple I] computer by
the author. There is no other source of much of the
information covered here, and the possibility of
error exists on the part of the author. For those
‘errors which do exist, the author is truly sorry.
‘The Apple IT isnota perfeet computer, and inthis
book, less than perfect features are reported along
with the more admirable features. There are many
opinionsof the author in the body of the textand the
reader must rely on his own judgment to evaluate
these opinions. Last the reader get a mistaken
impression from harsh comments about certain
‘Apple features, let the record be set straight here.
‘The author highly admires the Apple design and
considers this computer to be in a class by itself
Furthermore, he respects the newer produets being
designed by Apple. To Steve Jobs, Mike Markkula,
Rod Holt, and Mike Scott: "Thanks fellas.” To Steve
Wozniak: "Haw about an encore, Woz?”
Table of Contents
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Glossary
Appendices
A
B
é
D
E
F
G
H
1
3
kK
Schematie Diagrams
Index
Foldouts
THE APPLE II—AN OVERVIEW
BUS STRUCTURE OF THE APPLE IT
‘TIMING GENERATION AND THE VIDEO
SCANNER
‘THE 6502 MICROPROCESSOR
RAM IN THE APPLE IL
ROM IN THE APPLE II
ADDRESS DECODING AND INPUT/OUTPUT
VIDEO GENERATION
‘THE DISK CONTROLLER
MAINTENANCE AND CARE OF THE
APPLE II
References
‘Trademarks
6502 data
BASIC program listings
A logic cireuits primer
A number systems primer
Apple II revisional information
Historical notes
A technical conversation with Steve Wozniak
Baseplate and motherboard removal
List of Figures and Tables
Note of Caution
Several of the Application Notes in Understanding the Apple IT contain
procedures for modifying the Apple II computer and peripheral eards. Modi-
fieation of your Apple or peripherals may void your warranty if the warranty
period has not yet lapsed. It may also increase your out of warranty repair
costs should the modified unit fail in the future, The decision to perform any of
the modifications described in Understanding the Apple I rests solely with the
owner of the hardware concerned. Neither Quality Software nor the author
bears responsibility for any negative consequence of the owner's decision to
perform such modifications.
