C64-C128 CP-M Cartridge Interest

Tony Duell ard at p850ug1.demon.co.uk
Sat Dec 25 06:11:56 CST 2010


> 
> 
>     I'll try to ask a different question here
> 
>     What is needed to CREATE (and not build) a CP/M compatible computer?
> 
>     Now it got me puzzled. I have some circuit adaptations of MSX and TRS-80 
> computers, as minimal computers to run CP/M code. But what is needed - 
> beyond Z80 and 64K of RAM - to run CPM? Is there any kind of doc discussing 
> it? 

Actaully, AFAIK you don't need either of those...

An 8080 procesosr will do, so will an 8085 to run CP/M. However some 
application programs did use the Z80-only instructions so it probably 
makes a lot of sense ot sue that processor

You don't need 64K RAM. There have been 32K or 48K CP/M machines, it 
wouldn't suprise me if 16K was done too. Again, though, it's probably 
sensible to have 64K these days.

Unless you want to run a modified CP/M and applications, you need RAM 
starting at location 0. Since the Z80 starts at location 0 when you reset 
it, the normal thing to do is to have a boot ROM [1] that replaces RAM at 
locaiton 0 on resetm and is then switched out 9or relocated to the top fo 
the memory map) once the machine has loaded the OS into RAM.

[1] Some machines -- I think Cromemco was one -- had a little bit of 
hardware to force a jump instruction onto the processor data bus 
immediately after  rest, thus forcing th CPU to execute thr boot ROM at 
the tom of the memory map. Whether you want to call this a 'ROM at 
location 0' is up to you ;-)

You presumably need some kidn of mass storage. It doesn't have to be 
floppy disks. 

You need a text terminal or something equivelent to it. You can have a 
seiral port to a normal terminal, or memory mapped video, or whatever 
you like. 

And I think that's about it.

-tony



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