Date   : Mon, 15 Jan 1996 04:57:28 +0000 (GMT)
From   : John Sullivan <js10039@...>
Subject: Re: Illegal opcodes

On Tue, 9 Jan 1996, Tom Seddon wrote:
> At home I have an old Acorn User (I can't remember which issue) which 
> has a listing of all the 6502 illegal opcodes. Apparently they are 
> valid for 6502s marked 'SY6502A', and there is a small test program 
> to test if your 6502 implements the more useful ones. The 
> descriptions are also more helpful than 6502.txt (instead of LAX this 
> listing gives LDA-LDX for example) although it isn't as complete. 
> There are also no cycle timings, although these would be easy enough 
> to find out.
> 
> Is anyone interested? If people are I'll scan it in as a bitmap (the 
> page is black on yellow so it should come out OK) next time I'm at 
> home (end of January I should think) and e-mail it to people.

I think I have that copy, and it wasn't *that* useful - you still need
quite a bit of detective work to figure out what a particular opcode
means. 

Has anyone figured out Orlando's code from the Zalaga loader - as far as I
can tell the loader *code* jumps to the start of an ascii message which is
an author credit/copyright message. (Most of the start compromises
non-standard opcodes.) Presumably somewhere in this mess we jump to some
more sensibly code, but it's difficult to tell. It also looks like there 
might be a tune-player in there of sorts, but that's hard to tell also.

It's this sort of stuff we need to understand to get programs that rely on
it working. Orlando was a git. Very sharp, but nevertheless, a git.

John

-- 
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So much lonely, aching, empty shit.
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