Re: 6502 illegal opcodes questions

[Don Bruder <dakidd@sonic.net>]

In article <j7Wdne2Ir5coidDZnZ2dnUVZ_vydnZ2d@comcast.com>,
 "Michael J. Mahon" <mjmahon@aol.com> wrote:

> sicklittlemonkey wrote:
> > (From Linards)
> > 
> >>Is it documented anywhere which of these opcodes have which cycle counts?
> > 
> > 
> > Without checking, they should be the same as the corresponding LDA
> > opcode with the relevant addressing mode.
> > 
> > (From Marcus)
> > 
> >>There are some discrepancies between the different info files floating 
> >>around the net.
> > 
> > 
> > Yes, I've been collecting these, and collating the information for some
> > time.
> 
> Since there were several versions of the 6502, isn't it likely that
> some had *differing* illegal ops and results?

Not just likely - Absolutely certain. 

I've long since forgotten the source, but there used to be a listing of 
how the various "illegal" opcodes differed from chip version to chip 
version, and only a very tiny handful of them that worked on one version 
would work (or even do ANYTHING) on another version. 

(which, of course, is why they're "illegal" or "unsupported" or 
"undocumented" opcodes - You can't rely on them except on *THAT 
PARTICULAR CHIP*, and in some cases, not even then because the "what 
comes out the other end" can be influenced by the state of RAM, I/O 
locations, or other things that may or may not be duplicatable from one 
machine to the next!)

-- 
Don Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist,
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