Table Of Content• •
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'by Winston Gayler
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oward S ms 0,
4300 WEST 62ND ST. INDIANAPOLIS, INDIANA48268 USA
Copyright © 1983 by Howard W. Sams & Co., Inc.
Indianapolis, IN 46268
FIRST EDITION
FIRST PRINTING-1983
All rights reserved. No part ofthis book shall be
reproduced, stored in a retrieval system, or
transmitted by any means, electronic, mechanical,
photocopying, recording, or otherwise, without written
permission from the publisher. No patent liability is
assumed with respect to the use of the information
contained herein. While every precaution has been
taken in the preparation of this book, the publisher
assumes no responsibility for errors or omissions.
Neitherisanyliabilityassumedfordamagesresulting
from the use of the information contained herein.
International Standard Book Number: 0-672-21959~X
Library of Congress Catalog Card Number: 82-61966
Edited by: Welborn Associates
Illustrated by: D. B. Clemons
Printed in the United States ofAmerica.
Preface
This book is a detailed circuit description of the Apple II® computer. Specifically, it
covers the main logic board including all revision's from the earliest through the
latest (Rev. 0 through RFI Rev. D). Also covered are the current two-piece keyboard
and the older single-piece keyboard.
The intended audience includes engineers, technicians, students, and hobbyists.
An attempt has been made to appeal to most skill levels and backgrounds. Thisis
done by dividing each chapter into two sections: Overview and Detailed'Circuit
Analysis. You may choose to read one, the other, or both.
The book consists ofeight chapters. Chapter 1 discusses rremenclature and sym
bols used throughout the text and figures. This chapter alsocontains a glossary of
terms. Chapter 2 presents a description of the Apple II computer at the block dia
gram level.
The detailed descriptions start in Chapter 3. Chapters 3 and 4 cover the system
clocks and part of the video circuitry. Chapter 5 explains the memory system and
Chapter 6 examines the 6502 microprocessor and the system bus. Chapters 5 and 6
contain overview sections dedicated to the 4116 ~AM and the 6502 microprocessor.
Asa result, the reader need not have prior knowledge of these devices.
The keyboard and other on-board I/O are discussed in Chapter 7. The video
display (graphics and text) is the subject ofChapter 8. Much ofthe Apple's circuitry
serves to generate a video signal. Due to the importance ofthis topic, Appendix A is
included to provide an introduction to video techniques.
Appendix.B is a gathering ofall known circuit revisions ofthe Apple II mother
board and keyboard. While the body of the book describes the latest Apple II revi
sion, Appendix B describes differences between this latest Apple and all earlier re
visions. Appendix C contains a set ofmother board and keyboard schematics. These
schematics cover all revisions.'The book concludes with a list of references.
WINSTON D. GAYLER
EDITOR'S NOTE: In order to present the itlustrations as large as 'possible
many have been placed on the foldout pages at the back ofthe book. These
illustrations are indicated with an asterisk(*) immediately following the
figure number in the text, e.g., Fig. 3-4* indicates that Fig. 3-4 is located at
the back of the book.
I wish to thank fellow Apple enthusiast Dr.James Alinsky for his many suggestions
and general inspiration during the research and writing of this book. I am very
appreciative for his review, from the reader's viewpoint, ofthe complete manuscript.
Thanks also go to the numerous employees of Apple Computer, Inc., who as
sisted by providing documentation and answering questions.T appreciate the assis
tance of Apple's engineering department in coordinating much.ofthis activity.
Finally, I wish to acknowledge Stephen Wozniak who designed the Apple II,
making it all possible.
onten
CHAPTE,R 1
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9
The Audience-Chapter Organization-Trademarks, Patents, and
Copyrights-What You Should K.now-Revisions-IC and Signal
Nomenclature-Waveforms-Research-Glossary of Terms
C AP E 2
THE ApPLE II BLOCK DIAGRAM 17
Basic Architecture and Buses-Memory-Input/Output-Video-Power
Supply-Summary
CH 3
CLOCK GENERATOR AND HORIZONTAL TIMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24
Overview- Detailed Circuit Analysis- Summary
C AP ER 4
VIDEO TIMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 34
Overview-Detailed Circuit Analysis-Summary
CHAP ER 5
MEMORY SYSTEM 41
The 4116-0verview-Detaiied Circuit Analysis-Summary
CHAPTER
6502 AND SYSTEM Bus 58
()verview-Detailed Circuit Analysis-c-Burnmary
8 Contents
ON-BoARD 110 ··.................... 86
Overview-Detailed Circuit Analysis-Summary
THE VIDEO DISPLAY , '..104
Overview- Detailed Circuit Analysis- Summary
APPENDIX
VIDEO TECHNIQUES 139
The Basic Video Display-Broadcast Standards-Color-Overscan
Summary
APPEN IX
ApPLE'S REVISIONS ',. _ 149
Overview of Revisions-Detailed Circuit Analysis
AP EN IX
ApPLE II SCHEMATICS ' 162
Revisions- Symbols- Acknowledgments
APPEN IX
REFERENCES· 165
l""'t
INDEX ~ 168
'0•••••••••••••••••••••••••••••••••••••••••••••
Description:they are especially important in the Apple II due to their interplay with the video circuitry. Chapter 4 The random access memory in the Apple II is shared by the microprocessor and the video generator Next the color subcarrier W~~ ~elected to be an odd multiple (455) of half the hori- zontal rat
