SC204 – Z80 CP/M computer

This Z80 based modular computer runs CP/M 2.2 and also the Small Computer Monitor.

SC204 – Z80 CP/M computer

The complete system consisting of:

SC114 – Z80 SBC/motherboard
SC145 – Compact Flash interface module
SC301 – FTDI style USB to serial adapter and cables


  • Z80 processor runing at 7.3728 MHz
  • 128k bytes RAM (second 64k is not easy to use)
  • 32k bytes ROM
  • Asynchronous serial port (9600 baud)
  • Powered from USB to serial adapter
  • RC2014 bus compatible expansion
  • Small Computer Monitor (SCM) in ROM
  • BASIC in ROM

Optional Extras

A fast serial port is desirable. SC139 contains a 68B50 ACIA and this gives the system a nice 115200 baud serial port. It has its own onboard clock to make it independent of the processor clock speed.

SC139 – Serial ACIA (68B50) module

While the system can be powered from the USB to serial adapter, a better power supply can be useful. SC142 provides a regulated 5-volt supply from an 8 to 15-volt input. It also includes an on/off switch, a reset button, and a voltage supervisor/reset device. The voltage supervisor ensures the system gets a clean reset signal at power-up and when the reset button is pressed.

SC142 – Power supply and reset module

WARNING: The system should not be powered from two sources at the same time. Therefore, the serial port on SC114 should not be used with a powered USB adapter when the SC142 power module is fitted. In practice, this means you should get a serial module (eg. SC139) before getting the power supply module.

SC204 with SC139 serial and 142 power supply
SC204 extended with a modular backplane section

This is not currently available as a complete kit, but the individual modules are all available as kits on Tindie.

Documenation and Software


  • This design is made in accordance with the “designed for RC2014” labelling scheme.
  • RC2014 is a trademark of RFC2795 Ltd.
  • This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.

Homebrew 8-bit retro computing