2010-09-03

8-bit single board computers

Before I build my own single board computer, I wanted to do a study of past and "present" single board computers that "could" run CP/M, focusing in their features and capabilities. Since I like CP/M-80 and I already managed to build a few breadboard computers that could run CP/M from a floppy or memory, I thought could build something more permanent.
Most of the SBCs I've listed below are for the Z80, or derivatives.
  1. SB180 (from Micromint, details published on byte Sep-Oct 85 designed by Steve Ciarcia) uses a HD64180 (or Zilog's Z180) with 2 DMA channels, 2 Serial, floppy interface using FDC9266 (for high density disks) (update, I've changed the picture and here there's even a SB180FX).

  2. P112 uses a Z182 with 2 DMA channels, 2 full serial and a FDC37C665 for floppy interface, extra serial ports, parallel port and possible IDE drive (PC-style super IO, includes high density) (new version was being sold here, apparently there wasn't enough critical mass).
  3. CPU280 uses Z280 with 4 DMA channels, 2 serial ports and a FDC37C65 does the floppy interface (also high density disks), although some details can be found on the internet I was unable to find schematics.
  4. N8VEM (designed by Andrew Lynch) uses a vanilla Z80, serial port with 16C550, huge SRAM 512K (mostly used as a RAM-disk), big Flash Rom 1Mb with operating system (CP/M) included, ECB bus interface, Floppy interface is an external board (new design, several boards and developers here), RTC and parallel interface (i82C55) and it's all open hardware.
  5. YASBEC also uses Z180 but the hardware details are much more elusive in the internet, the disk format suggests 3.5 inch HD drives.
  6. PROF80 uses a Z80, has a floppy interface with the UPD765, high density data separator, bit-bang serial interface, on the webpage there are more details ans schematics of other boards (graphics terminal) and upgraded version with Z180 (with FDC37C68, RTC and other goodies) some more details here.
I think after that review, I can settle on what I want for my CP/M SBC with the 8085. A 3.5 inch floppy (HD), 765 Floppy interface, 8085AH-2 @ 10.24MHz (2% overclocked) a 8256AH, 128K SRAM and 32KB ROM (with a debugger, Forth or Basic and boot). On the optional is a second serial port, a parallel port, a SD Card interface and an expansion port. I think I can skip the RTC as CP/M 2.2 doesn't need it and it's optional for CP/M 3.0 .
Front panel inputs I'd like to have a RUN/HALT/SINGLE STEP switch on the front, a RESET push-button and an interrupt push-button (maybe RST7.5 or TRAP). As for indicators a RUN/WAIT/HALT (green/yellow/red) LED, a INTR/INTA (red/green) and a HOLD/HLDA (only if there's an expansion port).

1 comment:

Vitasam said...

Maybe it is good to mention this very interesting Z80 + FPGA single board computer:
http://www.retroleum.co.uk/v6z80p/