Re: 6502 illegal opcodes

On Friday 04 November 2011, you wrote:
> >> Opcodes $8b and $ab are not predictable in that their result
> >> depends on
> >> various analog effects; their behaviour can vary on a single physical
> >> chip when it heats up, even.
> > 
> > these are predictable though - if you choose the right argument :)
> > not that
> > ane #$00 is terribly useful =P
> 
> What is that, 8b?  Most people call that XAA afaik.

yes :) and XAA is long "deprecated" imho, only ppl who know it from the old 
broken lists call it like that =)

> >> Various opcodes are unpredictable in the sense that their result
> >> depends
> >> on what happens on the data bus while RDY is low.
> > 
> > i would not call that unpredictable
> 
> If you have full control over what happens on the bus, sure.  In most
> cases you do not -- it is specifically designed so you do not have to.
> 
> This also happens just for 8b and ab fwiw.  All other illegal opcodes
> are more or less sane, where 10xxxx11 is the "less" and the rest is the
> "more". (*)
> 
> 
> Segher
> 
> (*) Oh and of course the STX abs,Y and STY abs,X (9e and 9c) insns,
> those
> are naughty!

SHY and TAS you mean =) those are which i ment - they work perfectly if you 
make sure nothing else tries to access the bus :) (and unlike ANE, they are 
sometimes useful)

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