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Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!hplabs!hp-pcd!john
From: john@hp-pcd.UUCP (john)
Newsgroups: net.micro.apple
Subject: Re: Undocumented 6502 Opcodes
Message-ID: <20000004@hp-pcd.UUCP>
Date: Wed, 13-Mar-85 16:37:00 EST
Article-I.D.: hp-pcd.20000004
Posted: Wed Mar 13 16:37:00 1985
Date-Received: Fri, 15-Mar-85 05:33:22 EST
References: <376@aicchi.UUCP>
Organization: Hewlett-Packard - Corvallis, OR
Lines: 16
Nf-ID: #R:aicchi:-37600:hp-pcd:20000004:000:790
Nf-From: hp-pcd!john    Mar 11 13:37:00 1985

<<<<
  I once found a bunch of undocumented opcodes in the 6502 in my KIM-1 by
looking for patterns in the opcodes. None of the original  6502 opcodes ended
in 11 (as in XXXXXX11). It turns out that executing these instructions would
perform both a XXXXXX01 and a XXXXXX10 instruction. For example a A7 would
load X from Page Zero (A6) AND load A from Page Zero(A5) at the same time.
There were also some store instructions that could OR two registers and
store them in memory in one instruction although I hate to think what  was 
going on inside the chip for that one.

  I am sure that if a HCF was a opcode 12 that it must have been a special
case instruction. Its class and grouping is what you would have suppected a
ASL (ind),Y to be if it existed. 

John Eaton
!hplabs!hp-pcd!john