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Date   : Mon, 09 Sep 2002 20:23:37 +0100
From   : Sprow <news@...>
Subject: Re: 65C102 thousand dollar question

In article <KNEEJIOPPHNNBHBMMGACAEBKCDAA.ricky@...>,
   Richard Gellman <ricky@...> wrote:
> I'm having a problem with second processor emulation.

> Something keeps trying to execute opcode &FC on a regular basis.

> Unfortunately, this is not a valid opcode :)

> &FC is NOP Abs,X on the 6502 (undocumented), but behaves differently on the
> 65C102.
>
> I've tried a few tests, and with simple data in A, X, and Y, the 
> instruction doesn't seem to do anything.

Where abouts is this magic &FC? There are an awful lot near the top of ROM
in the vector tables.

The only instructions that I know got added to the 65C102 over the 6502 are
PHX,PLY,PHY,PLX,BRA,STZ,TRB,TSB and RMB/SMB to reset and set memory bit and
BBS/BBR to branch on given memory bits being clear or set.

I've checked the opcodes for all but the RMB/SMB and BBS/BBR so it's not
those,and dasmx 1.30 (though supporting the 65C102) doesn't understand it.
I input 0xFC 0x01 0x01 0x01 and got
 db &FC <-shame
 ora (&0001,x)

Sprow.
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