Path: utzoo!utgpu!watserv1!maytag!xenitec!zswamp!root
From: root@zswamp.fidonet.org (Geoffrey Welsh)
Newsgroups: comp.sys.cbm
Subject: Re: Undocumented 6502/6510/8502 instructions?
Message-ID: <4795.2748BCB7@zswamp.fidonet.org>
Date: Mon, 19 Nov 90 23:02:57 EDT
Organization: Izot's Swamp BBS - Kitchener, Ontario

>In article <1990Nov17.185259.10564@evax.arl.utexas.edu> 
>cs4344af@evax.arl.utexas.edu (Fuzzy Fox) writes:
>>The 6502, 6510, and 8502 are all internally the same as far as
>>instruction processing goes, so the illegal opcodes generate the same
>>effects on all three CPU's.

Pasi 'Albert' Ojala (po87553@korppi.tut.fi ) wrote:
 >I will surely disagree. The real reason for crashing was the fact that
 >undocumented commands did't work on 8502 at all. At least all these so
 >called undocumented op-codes were 'accidents' produced by the other
 >commands and the processor design. I am sure that both 6502 and 8502
 >differ significantly in their inner design.

   I don't think that I will reveal any deeply-kept secrets when I say that 
PaperClip II used undocumented op codes in its descrambling (copy protection) 
routine... the same codes used by the 64 version, which were in turn from 
6502-derived tables.

   Similarly, DesTerm 128 used 6502-derived op codes for its descrambling. 
They behaved predictably.

   Since Steve Douglas, Matt Desmond, and I have all been able to use 6502 
undocumented ops on the 6510 and 8502, I'm willing to state with some 
confidence that most of the useful codes work identically (or at least, very 
similarly) on all three CPUs.
 

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