24 Aug
1999
24 Aug
'99
8:58 a.m.
and the
vendors would make sure they were there.
This is fine if you're a large company and can specify the 'undocumented'
behaviour of a chip. For a one-off hacker like me, it's a little more
dangerous. AFAIK, all Z80s did the same thing with undocumented
opcodes, and it was
safe to rely on them. But I've met devices (not CPUs specifically) where
later/second-source versions have had different behaviour under
'undocumented' conditions, so I learnt the hard way to be careful.
My reference for 8085 and z80 is however limited to them but, for all
vendors of those parts (and versions thereof) that I know of it's true.
Timing differnces are more common.
allison