SC118, v1.1, Description

SC118 is an easy to build Z80 Single Board Computer card.

The aim of this design is to make entry into the Z50Bus universe as easy and reliable as possible. This is achieved by using relatively few components, and thus minimal soldering. There are also no configuration jumpers to worry about.

This card can work in a modest way as a single board computer (SBC), without even needing a backplane, yet can easily be expanded to run CP/M and more.

Here are the specs:

  • Z80 running at 7.3728 MHz
  • 128k bytes RAM (second 64k not easy to use, so best consider it to be 64k usable)
  • 32k bytes ROM, which can be paged out with the usual write to port 0x38
  • Simple bit-bang serial port to get you started
  • Four RC2014 standard bus sockets
  • Reset button
  • Voltage supervisor for clean reset
  • LED for power and status indication
  • Runs the Small Computer Monitor, with ROM BASIC and the CP/M loader included

The idea is that you first build the board and tested it as a single board computer.

Next you build a Z50Bus backplane and check the processor card still works when connected to the backplane.

The next step would be to build and test a proper serial port, which gives better performance and compatibility with the current CP/M distribution.

Then if you want CP/M all you need to add is a Z50Bus Compact Flash adapter and a Compact Flash card with a suitable CP/M distribution installed. All this is supported by the ROM with no configuration required.

Homebrew 8-bit retro computing