[A83] Re: microcode

To: <assembly-83@lists.ticalc.org>
Subject: [A83] Re: microcode
From: "Henk Poley" <HPoley@DDS.nl>
Date: Sun, 9 Sep 2001 19:13:48 +0200
Reply-To: assembly-83@lists.ticalc.org


> Van: Sebastiaan Roodenburg <sebastiaan@rimsystems.nl>
> 
> > Is it possible to make something in microcode?
> > (these are the individual instructions which are
> > executed with a z80 instruction)
> 
> Nope... microcode is coded into a little piece of ROM inside the Z80, and
> since ROM can't be changed... (maybe it can be done with a hardware
> hack, but i doubt it)

Yesterday I found a book my grandfather used when learning to program, it
handles the i8080 (horrible syntax), Z80 and M6800 (that's not the M68000
from the Ti89/92[+]). Somewhere in the book I've found some things about
microcode, so I'll take a look... Don't give you much of a chance it can be
done, as far as I have read (Thomas Scherrer's hompage) the Z80 is one of
the biggest CPU's which are "hardwired", which says as much as, "it doesn't
use microcode".

Could be that it does work with microcode, but then the problem arises that
it wasn't that common to have reprogrammable ROM's, just because they were
to expensive. I don't think that Ti has made an effort of getting a
'reprogrammable' Z80... Most of the time Ti has chosen for the safer
option, I don't thing that they want people to accidentally change their
processor when trying 'secret' OP-codes, or crashing when their calc. And
btw, what need would it have for Ti to be able to update the processor, one
that has been used for about 20y by now?

	Henk Poley


BTW: what was the mail you replied to? (did I miss something?)