H89 CP/M hard-secored boot diskette

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Apr 4 18:39:29 2003

> Hi
> I guess the next question is, does anyone have the
> dumps of these chips or what the new mapping is??

I have dumps of all the programmed chips in my Z90...

> I suspect that there is some remapping of the memory
> and some for the I/O. I don't know why it would take
> 3 chips though. I'll have to dig through my stuff to

AFAIK, the 3 chips involved are the monitor ROM (Z80 code), the memory
mapping PROM and the I/O mapping PROM.

> >2) Connect a jumper from the middle pin of U503 to pin 17 of P509

I believe that's the mod I mentioned which connects an output port line
to the input on the memory mapping PROM, thus allowing software selection
of HDOS (ROM at location 0) or CP/M (RAM at location 0) memory maps.

Received on Fri Apr 04 2003 - 18:39:29 BST

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