SC708 – RCBus Z80 SBC Module

SC708 is a Z80 Single Board Computer (SBC) module designed for the RCBus. It is CP/M, just add a backplane and a Compact Flash module.



Nothing known


KitsWebsiteShips from
Stephen C CousinsTindieUK
PCBsWebsiteShips from
Stephen C CousinsTindieUK
Assembled and TestedWebsiteShips from
Not available
See parts list

Parts List

PCB1SC708, v1.0, PCB
C1 to C66Capacitor, ceramic, 100 nF
LED11LED, green, 3mm
P11Header, male, 2 row x 40 pin, angled
P21Header, female, 1 row x 6 pin, angled
P31Header, male, 1 row x 6 pin, angled
R11Resistor, 1k, 0.25W
R2 to R76Resistor, 10k, 0.25W
SW11Switch, tactile button, angled
Screw (for spacer)1Machine screw, 6mm, M3
Spacer1Spacer, 10mm, M3, nylon
U11Z80 CPU, Z84C0008PEG, or
Z80 CPU, Z84C0010PEG
U21RAM 128k bytes AS6C1008
U31FLASH 128k bytes SST39SF010A
X11Oscillator 7.3728 MHz
IC socket 40-pin
1Socket, DIP, 40 pin
IC socket 32-pin
U2 and U3
2Socket, DIP, 32-pin
IC socket 14-pin
1Socket, DIP, 14-pin
IC socket 16-pin
1Socket, DIP, 16-pin

Printed Circuit Board


This module conforms to the RCBus specification v1.0 for RCBus-2014 and RCBus-Z80.

User Guide

SC708 is a Single Board Computer (SBC) meaning it can work without any other backplanes or modules. It is based on a Z80 CPU running at 7.3728 MHz, with 128k bytes of RAM, 128k bytes of FLASH ROM (only 32k bytes is usable), and a simple bit-bang serial port. As a single board computer it is powered from the serial port.

The kit includes the Small Computer Monitor pre-programmed into the FLASH ROM. This includes a capable debug/monitor, BASIC, and a CP/M loader.

As there is no power-on reset circuit on this module, it is necessary to press the reset button to begin executing the firmware.

The board is CP/M ready, meaning it has a suitable processor and memory to run CP/M. Just add a backplane and a Compact Flash module to run CP/M. Ideally, a serial port module should also be added.

Input/output port functions
I/O Address ReadWrite
(0x08 to 0x0B)
n/aStatus LED (LED 1)
Low = ON, high = OFF
(0x20 to 0x23)
(0x28 to 0x2B)
(0x30 to 0x33)
n/aRAM bank select
(0x38 to 0x3B)
n/aMemory paging (lower 32k)
Low = ROM, high = RAM
Jumper options

Clock oscillators X2 and X3 are optional. The default is to connect the output of clock oscillator X1 to the CPU and the RCBus CLK pin. This requires a jumper shunt in each of the two marked default positions (JP1.1 and JP1.4). If you wish to use a clock sourced from a different module then the X1 jumper should be removed.

Fit a jumper shunt to JP2 if the voltage supervisor is to be used. This jumper connects the voltage supervisor to the RESET signal. The system should only contain one enabled supervisor, thus the jumper has been provided to isolate or connect this device.

Assembly Guide

Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.

  1. Header socket P2
    This should lay flat against the PCB
  2. Resistors R1 to R7
    These can be fitted either way around
  3. Decoupling capacitors C1 to C6
    These can be fitted either way around
  4. Sockets for U1 to U5
    Fit such that the notch in the socket matches the curve in the outline on the PCB silkscreen
  5. Bus header P1
    Make sure the pins are parallel to the PCB so that the board is vertical when it is fitted into a backplane socket
  6. Header pins P3
    Ensure the pins are parallel to socket P2
  7. Light emitting diode LED1
    Fit such that the short lead and/or small flat on the plastic is at the end marked with a line on the PCB silkscreen
  8. Reset switch SW1
  9. Oscillator X1
    Ensure the orientation matches the PCB silkscreen, noting the sharp corner at pins 1
  10. Insert the integrated circuits into their sockets
    Make sure the notch in the component is at the end indicated by the notch in the socket and the curve on the PCB silkscreen
  11. Fit the nylon spacer in the mounting hole


  • This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.
  • The product contains small parts and is not suitable for young children.

Homebrew 8-bit retro computing