On Jun 7, 13:05, Richard Erlacher wrote:
> You may be confused about this. I don't know of a single NMOS 6502 that
> didn't adhere to the MOS-technology instruction set. There's no telling
> whether that included the undocumented opcodes, but since Synertek and
> Rockwell used the MOS mask set, I suspect there was no difference. The
later
> Synertek parts may have been different since they shrank the die and got
a bit
> more speed, offering a 4 MHz 6502-C, which was an NMOS part and worked
> perfectly in NMOS-targeted systems that didn't work with the later CMOS
parts.
There certainly were differences between the sets of undocumneted opcodes
from different manufacturers of 2MHz 6502A parts. I remember one or two
"clever" bits of software that failed on some BBC Micros for that very
reason. Sean is absolutely right to avoid undocumented codes.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Fri Jun 07 2002 - 18:17:13 BST