Re: 6502 illegal opcodes questions

[heuser.marcus@freenet.de]

sicklittlemonkey wrote:
>
> The Apple-based research doesn't differ much from the more detailed
> research done on the C64, Atari and even BBC systems. It seems that
> this is because the same MOS 6502 mask was used for the 6510 and other
> 6502 implementations.

As the 6510 is a MOS chip this doesn't come as a shock, really  ;o)
And it explains why "illegal opcodes" are so much more popular on the
C64: Only one chip version in all these years (though under different
names).
AFAIK the 6502's in the Ataris were compatible to each other, too.

> In any case, some Apple games use these opcodes, and many more C64
> games do. Although a multibyte NOP is often sufficient, in other cases
> the expected operation is required, not hard to implement, and improves
> emulation authenticity (e.g. crash behaviour).

I agree with you here, Nick. Documenting them as thorough as possible
is definitely important, as they were used.
On the other hand I haven't seen an application where they were
indispensable.
Does anybody have some interesting sources they would share (or can me
point to some)?

bye
Marcus