7 Jun
2002
7 Jun
'02
2:17 p.m.
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