Date : Thu, 23 Jul 1992 03:30:20 GMT
From : daffodil!wyvern!alpha@ames.arc.nasa.gov (Joe Wright)
Subject: Re: Undocumented Z80 Opcodes
sage@LL.MIT.EDU (Jay Sage) writes:
: Willy answered me with:
:
: >> Both the '180 and '280 have expanded instruction sets that make use of
: >> the so-called un-documented instructions, particularly in the ED-xx
: >> group...
:
: Thanks for the reply, but I did not completely understand it. I knew, of
: course, that the Z180 and Z280 had expanded instruction sets, and I would
: have guessed that most if not all of the so-called undocumented Z80 opcodes
: would have been used. The question is, do none, some, or all of the
: formerly undocumented codes work on the Z180 and Z280 chips as they do on
: the Z80? If some program authors made use of those undocumented opcodes,
: will their programs no longer work properly?
:
: -- Jay Sage
:
Imposter? :)
The Jay Sage I know has both Z80 and Z180 machines at hand. My Jay would
be answering these questions instead of posing them. (Just kidding Jay.)
But the question of whether undocumented (read unsupported) opcodes work
or not is moot. If you use them on your Z80 machine and they work for
you at 'your house' there is no reasonable assurance that they will work
the same way on a Z80 at 'my house' (though they probably will). And if
they don't, there is nobody to complain to (except the author of the
'broken' code). The Z180 began life as a Hitachi 64180 and has nothing
in common architecturally with the Zilog Z80. If any 'undocumented'
Z80 ops produce the same results on a 180 it would be by accident rather
than plan. And you wouldn't actually use them in a program would you?
It is academically interesting I guess. Somebody (not me) ought to
document the undocumented opcodes for both processors and compare the
results. Offer all results to the net and/or znode and rcpm systems
and stand back. There are still a few hackers out there who will test
what you say and confirm or argue against your conclusions. It might
be fun. But maybe not important. You wouldn't use them!
--
Joe Wright alpha@wyvern.twuug.com