Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!wuarchive!mit-eddie!bloom-beacon!eru!hagbard!sunic!isgate!krafla!adamd
From: adamd@rhi.hi.is (Adam David)
Newsgroups: comp.arch
Subject: Re: Zilog's mnemonics; a boon to programmers
Message-ID: <2418@krafla.rhi.hi.is>
Date: 18 Nov 90 14:28:42 GMT
References: <1990Nov16.050844.12539@hayes.ims.alaska.edu> <3073@cooper.cooper.EDU>
Organization: University of Iceland
Lines: 43

In <3073@cooper.cooper.EDU> gene@cooper.cooper.EDU (Gene (the Spook) ) writes:

>According to every source for the Z80 (as far as I know), all these
>pseudo-instructions worked just fine, but were neither tested-for
>nor guaranteed.

Some of them have it, and some of them don't. It depends on the manufacturer
and which revision of the silicon.

>Also, if I'm not mistaken, the Z[12]80 support similar operations.

Well, yes and no. Both chips have an undefined opcode trap, which calls an
exception routine if the instruction is not defined.

According to the Z180 manual, no instructions are defined to access IXH, IXL,
IYH, IYL or "shift left and set" operations. These would then be diverted via
exception handler but the only practical reason for emulating them is to test
software for another system which does support them as opcodes.

The Z280 supports all the opcodes which access individual bytes of IX and IY.
There are also many new instructions and some new addressing modes, for instance
SP and PC relative modes, base+index addressing. JP and CALL relative, index
with 16-bit displacement, etc. etc. etc. There is good multiprocessor support in
hardware. The "shift left and set" instructions no longer exist though, and
have been replaced by "test and set". This change can be used to determine which
CPU is present. The undocumented Z80 opcode for IN F,(C) is also official on the
Z280 but is renamed and might therefore have changed slightly.

>Play with them and have fun!

Yes, there may well be several other useful instructions hiding in the Z80
(and probably different ones depending on whose Z80 and which one).

>(BTW, try to get hold of an old 6502 and use the HCF (halt and catch
>fire) instruction.  Loads of laughs.  Impress your friends.)

I guess the Z80 is more robust than this (?).

BTW, does anyone know what happened to the NEC V25 chip? That was the 8086 with
a Z80 compatibility mode.


Adam David.       adamd@rhi.hi.is