17 Apr
1999
17 Apr
'99
3:07 p.m.
about those undocumented opcodes . . . I didn't pursue what happened to them
in the UMC, VLSI, SYNERTEK, Mitsubishi, or WDC (WSI) parts. I heard rumors,
but wasn't concerned about it then. After 1982 I only used the ROCKWELL
CMOS parts. Rockwell took care of them by getting rid of them. Of course
they expanded the instruction set as did several others.
Dick
-----Original Message-----
From: Allison J Parent <allisonp(a)world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Saturday, April 17, 1999 1:42 PM
Subject: Re: z80 timing... 6502 timing
The 6502 series had all sorts of undocumented opcodes
and they tended to
change with later versions.
Rockwell made a specific point about the undocumented opcodes in their
version, in that all the unimplemented opcode values in their CMOS parts
were NO-OP's.
<THe 65xx stuff is quite known, but what has been
new to my ears are the
<8085 'hidden' operations.
Those were more useful as the 8085 had some rather open holes in the
instruction set. The z80 also had a raft of them all commonly supported
though officially unofficial. and none were compatable with the 8085 hidden
ops (in either direction).
Allison