H89 CP/M hard-secored boot diskette

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Apr 3 18:45:00 2003

> > The Z90 is built to be 64K a H89 isn't. As far
> > as I recall, the H89 took more than a simple jumper or
> > switch to make it CP/M compatable.
> > Also, one should note that HDOS came in both hard and soft sectored.
> > Dwight
>
> Dwight, I think you're right. Address decode is controlled by U516 and U517
> on the CPU board... and those are PROMs of Heath's creation... close to

I have, of course, dumps of the 2 proms (one is 32*8, the other 256*4) in
my Z90. They're a lot less 'unobtainium' than many chips I deal with!.

> unobtainium. I have several different versions of each of these PROMs, but
> I haven't yet figured out their contents and differences.

IIRC, there were modified PROMs for CP/M-capable machines, which allowed
the memory to be re-mapped with RAM at address 0. Older version CPU
boards need a jumper wire (from an output port bit to a pin on the PROM,
basically) for this, I think it's a trace on later boards.

> Tony, out of curiousity, what are your versions of the various PROMs and
> EPROMs at U516, 517, 518, and 520 on your Z90?

That would involve getting to the Z90, which is not going to be trivial....

-tony
Received on Thu Apr 03 2003 - 18:45:00 BST