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_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 ower. sme ntrmation icing aon scone 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 eomputer 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 companies 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 computer: 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 achieving 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 technically 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 operational 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 includes 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 programming 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 modification, 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 available 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 modifications 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.