Re: 6502 illegal opcodes questions

[John Selck <selck_j@informatik.hgv-hamburg.de>]

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

If we're talking of normal 6502's, then there are almost no differences 
on the illegal opcodes. There are ofcourse extended versions of the 6502 
like the 65CE02 or the 65C02, but these don't count since also the 
documented opcodes have changed...

If we're talking about the illegals and differences, the only thing 
which usually is different is the stability of some illegals, but if you 
know about these it is safe to use the stable ones or cancel out the 
unstability (by ANDing with 0's for example).