Hand-rolling a CP/M machine

Chuck Guzis cclist at sydex.com
Tue Apr 24 15:28:49 CDT 2007

On 24 Apr 2007 at 14:29, Ethan Dicks wrote:
> > NSC800 run it if you got one.
> Don't know that one - what makes it special?

Basically 8085 timing with a Z80 instruction set in CMOS (has a low-
power "sleep" mode).  I've got a few (maybe 20) of the 2.5 MHz parts. 
 Love to get my hands on a couple of the 4 MHz parts.  There was an 
article in one of the mags about retrofitting one into a CompuPro 
85/88 board.  There are some signal inversions and a few timing 
issues requiring some extra glue, but it's an interesting way to 
upgrade an 8085 box to run Z80 code.  There is an extra configuration 
port at (IIRC) I/O address 0bbh, so you have to be careful to avoid 
collisions with existing port usage.  The good news is that said port 
responds only on OTI/INI instructions and not the 8085-style OUT and 
IN (immediate port address) instructions.

I've had lousy luck getting one to work with an 8202 DRAM controller, 
however.  Runs fine from ROM and gets very sick the moment it sets a 
toe into DRAM.  One of these days, I'll hang a logic analyzer on it 
and figure out if it's fixable.


More information about the cctech mailing list