68000,68010 and 68020 Primer Stan Ke ll y-BootIe and Bob Fowler Howard W . Sams & Co ., Inc . A Subsidiary of Macmillan, Inc. 4300 West 62nd Sireet, Indianapolis, Indiana 46268 U.S.A. " 1985 by n.. IMliIe GrouP. Inc. f1RST EO!TJON SECOND PRlNTING-I987 AI rIt,jIl$ ~ fib pill" ollhis book 5MII be reprockxed. SIQI\'d in ;, Te!!leval ¥\mI. or mmsmlned by IIOJ me;'ll$. 1kctn:ric:. ll'lI!CMniciIl, photocopying. recording. or CIIIle!I.uise. withoutllllinen pemtlssio. from me publlshal fib pillenI Iiobllily Is lIS5Umed with respect I() me use of me In!ormalion conIaIned herein. While e\Il'fY prtc.IIulion I>M been taken In me pref)II~tion ollhls book. me publi5her llSSUme5 no responsibility lor errors or omIsIons. Neltha Ii ;,rt,'lIobitily aswmed lor dam;,ges resul~ng from me use of me information conUIlned hereon. The w;'lle Group hM rnbde eue.y ;,nemplto wpply tradmlari< Inlormalion ;,00..1 CQIllpiI", 1'WTOI!5. ~ iIIld seMces mentioned In IIlIs book. The ~ indicated beICJo,r.o were derived from worious to.,,~es. The w;'''e Gn:Iup Cilnnot ;,nesl I() the IOCCUIllCll ollh'$ Informlltlon. 808O.8088I8086;,nd Intel III'\! I~rb ol lnlel Corporlltlon. AM· t oo Is;, registered 1I'!lderMri< 01 Alpha Mkrosystems. Inc. Apple Is II 1rlsde1'Tl!lri< 01 Apple Computer, Inc. EXORciser. EXORtnbCI. EXOOset. VERSAmodules. ;,nd VMErnOO..oIe$ 11m mg1s10'ed ~rk$ 01 MoIOfda. Inc:. IBM;,nd IBM PC III'\! tr!>demlln.s oI lnlernalion.lJ Businoess M;ochlne$., Inc:. l..otus, 1-2·3. and Sym~ are Ir'a!IerMrks of Lotus ~I ~Iion. MlIdnlosn Is II trlIdetnD.ri< 1Ic~ 10 Apple Compu~ Inc:. MBASIC Is a reglsleNd 1l'lIdemari< of MIr:r<.>soft Corporation. R6dio Sllack Is a reglSlefed 1Ji\demilri< 01 R6dio SIlack. VobrdSt;,r Is ;, m9siered 1l'lIdemari< ol MiaoPIo lntem/ltiorwll Caporalion. Z80 Is a ~ trademari< of Zilog. Inc. Inlernatiorwll Standard Bcd Number 067·224a.-4 LJbolIry of Congrew Catalog Card Number: 85-61636 TypogrlIIlhy by W;,I\oer Graphoc:s Pffrud In the lkIi!ed SfoIes 0/ Ammca To my childers everywhere: Edmund Paul, Michele Rose, Carol Ann, David Russell and rather late, alas, Anna Clare -SIan Kelly-BooOe To Curuprem Singh Khalsa, whose encouragement, inspiration, and vision over the years have helped to prepare me for this task - B.F. Acknowledgments We v.oere templed for a while to break with tradition , and claim that this book was entirely our ()VJn v.ork, conceived, written and produced with no outside help whatsoever! I-bnesty and chivalry, though, combined with threats from certain quarters, finally convinced us that we should pay oor respects in the customary manner. First, we must thank Motorola's MOS Integrated Circuit Group without whom (as they say) our primer \.IJOUld undoubtedly be devoted to a less inter· esting and rewarding family of chips. In particular, we are grateful to James J. Farrell III , Technical Communications Manager, and Margaret Dickie at Motorola Inc., Austin, Texas for their coorteoos help with permissions, pictures and diagrams. Our debt to writers on the M68000 and 16/32 bit micros in general is enonnous and must here be condensed to a simple, nonexhaustive enumeration: Stritter, Treddenick, Scanlon, Starnes, Kane, Hawkins, Leventhal, Alexandridis, Waite, Morgan. Editorially, \Ale received encouragement from James Rounds of t-IovJard W. Sams & Co., helpful advice from DI: Roger C. Gledhill of International Micro Technologies, Inc., and much-needed cajolery from Mitch Waite and Jerry \-blpe of The Waite Group. On the production side, \Ale would like to thank lynella Cordell and her staff at The Waite Group, who together with Marla Rabinowitz and Walter Lynam resolved the maT>/ typographical and stylistic problems created by our keystrol