0 - Homebrew CP/M Microcomputer

Author: sgeorge, Posted on: 15 August 2015 21:24

So, I have for the last year or so been slowly taking notes on another long dreamed of project, that of building a microcomputer from the ground up. My design keeps flip flopping between some game style computer (C64 style) to full on 'computer' computer like an S-100 bus computer.

My ultimate goal is to boot up into basic, and have CP/M ported over.

I'll be using a Z80, because I never had a Z80 computer before, I had C64's, Amiga's, PC's etc but never a real Z80 computer (OK, I do have a C128 with a Z80 in it but its very clunky to actually use the Z80).

I dont want to just buy an old S-100 box or a new N8VEM PCB.

So, the fundamental question is do we do a computer with a bus (aka something with our own bus thats like an S-100 computer) or something thats 'fixed' and more like a C64.

Expandable or non-expandable basically.

Right now I'm leaning toward multi card pcb using Eurocard connectors (3 row, 96 pin) because I have a buch of male/female connectors I can use up.

I do know I want CP/M running on it.

There will be a PIC doing double duty as an MMU so I can bank 4kb RAM pages in and out, and I'll have a 24bit address range with up to 16mb ram, this lets me map ram in for video, sound, disk drives etc. It will also be talking to a cool 2 line VFD I have that will go on the front of the case. VFD always have a cool retro feel.

I have for sound old school OPL2 Yamaha (YM3812) chips and (YM3014B) dacs, and for video I have some VGA DAC chips that I should be able to use to drive a VGA display with 256 colours at low resolution.

SNES controller PCB sockets for two SNES game controllers.

Books were looking at;

  • How to build your own Microcomputer (1980)
  • S-100 Bus Handbook (1980)
  • Interfacing to S-100 Microcomputers (1981)
  • The S-100 and other Microbusses (1981)
  • Build Your Own Z80 Microcomputer (1981)
  • Designing Microcomputer Systems (1979)

These are all interesting from a bus design perspective.

I think the hardest thing is going to be getting video output at speed.

This is something thats.. long in the tooth. I have been taking notes for a long time on and off, and nothing is really going to happen for a while. (Too many other projects going on right now!)

tags: CP/M, Microcomputer, Z80


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