24 Dec
2010
24 Dec
'10
8:13 p.m.
> 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?
On Fri, 24 Dec 2010, Dave McGuire wrote:
Very little is required beyond a CPU and memory.
First, a Z80 isn't
required; you can use an 8080 or an 8085. (or one of the later Z80
implementations) You also don't need 64K; CP/M will run in much less,
16KB I think was the minimum.
Beyond that, you need some sort of ASCII textual console device (like
a serial port, or a video subsystem + keyboard interface) and a
mass-storage device.
That's it!
Well, . . . CP/M kinda assumes that it will have contiguous RAM for its
TPA, starting at location 0 (The "relocated" CP/Ms for UNMODIFIED TRS80
don't really count) That means that in general, the BIOS (usually ROM)
needs to be at the top, and I/O should stay out of the way (avoid memory
mapped I/O anywhere but the top)
The BIOS is the key to being able to use all kinds of bizarre hardware.
The BIOS needs to be able to do console I/O a character at a time, and
block I/O (disk "sectors" that don't really need to be disk nor sectors)
128 bytes at a time. Study the source of some BIOS's - if you can create
a CPM compatible BIOS for it, then it is CP/M compatible.
(the above statement is a little over-simplified)