SC111, v1.0, User Guide

The SC111, Z180 CPU module can be used in two basic ways.

  • Z180 native mode. This requires a matching Z180 Memory module, such as SC119, which provides 1 Megabyte.
  • Z80 replacement mode. This allows use of 64k style memory modules, such as the RC2014 64k RAM module and the RC2014 pageable ROM module.
SC111, Z180 CPU (front), plus SC119, Z180 Memory (back)

Both modes support the Small Computer Monitor and ROM BASIC, and both can run a suitable versions of CP/M. Z180 native mode also supports RomWBW, which provides a wealth of hardware support.

Firmware Options

Z180 native mode firmware:

  • Small Computer Monitor, configuration S5
  • RomWBW

Z80 replacement mode firmware:

  • Small Computer Monitor, configuration S4

Software Options

Z180 native mode software:

Z80 replacement mode software:

  • After starting from SCM S4, most software for RC2014-Z80 should run.

DCD Input

A jumper shunt should be fitted to JP9, as illustrated below.

Some versions of the Z180 require the DCD input to be low for the serial port to work correctly. Other versions allow the serial port to operate with the DCD input either high or low. In the latter case, this pin can be read in software making in a general purpose input. To allow for all versions of the Z180 a jumper shunt should be fitted to JP9, pulling the DCD input low.


A system using this module can be powered from the backplane, or from either of the built-in asynchronous serial ports.

Each serial port, highlighted below in red, can supply power to the system. To connect power from a serial port, fit a jumper shunt in the appropriate location, indicated below in yellow. The top jumper is for port A and the bottom jumper is for port B.

Power from serial ports

WARNING: You should normally only connect one power source to the system, at any time.

As power can flow either way, these jumpers also enable serial devices to be powered from this module. If such devices are used, fit a jumper shunt in the appropriate position, indicated above in yellow.

Serial Port Clock Source

Current firmware and software for this module assume the built-in serial ports use the main processor oscillator (X1) as their clock source. However, the module allows a separate oscillator (X2), shown below in red, to be used instead.

If you wish to experiment with this option, fit a suitable oscillator in position X2. Also, fit jumper shunts to both JP7 and JP8, indicated below in yellow. In addition, you will need appropriate firmware to match. This requires study of the CPU’s datasheet!

Do NOT fit jumper shunts to JP7 and JP8 when using ‘standard’ distribution firmware and software designed for this module.

In normal operation, just leave this header unconnected.

Clocked Serial I/O

The CPU’s built-in clocked serial I/O port is available at the connector P4. This has to potential to provide a fast SPI, or similar, port, but requires appropriate software.

In normal operation, just leave this header unconnected.

Homebrew 8-bit retro computing