SC714 – RCBus Z80 Memory Module

SC714 is a memory module with 512k bytes of FLASH ROM and 512k pages of RAM designed for the RCBus. This module provides suitable memory for running RomWBW and CP/M.



Nothing known


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

Parts List

PCB1SC714, v1.0, PCB
C1 to C66Capacitor, ceramic, 100 nF
JP11Header, male, 1 row x 3 pin, angled
Jumper1Jumper shunt
P11Header, male, 2 row x 40 pin, angled
Screw (for spacer)1Machine screw, 6mm, M3
Spacer1Spacer, 10mm, M3, nylon
U11FLASH 512k bytes SST39SF040
U21RAM 512k bytes AS6C4008
IC socket 32-pin
U1 and U2
2Socket, DIP, 32-pin
IC socket 20-pin
U3 and U4
2Socket, DIP, 20-pin
IC socket 16-pin
U5 and U6
2Socket, DIP, 16-pin

Printed Circuit Board


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

User Guide

SC714 provides 512k bytes of banked FLASH ROM and 512k bytes of banked RAM, together with paging control of the lower 32k. This configuration is suitable for running RomWBW and CP/M.

The top 32k bytes of the 512k byte RAM are always mapped to the top 32k bytes of the Z80’s memory space (0x8000 to 0xFFFF).

At reset the bottom 32k bytes of the 512k byte FLASH ROM are mapped to the bottom 32k bytes of the Z80’s memory space (0x0000 to 0x7FFF).

Any of the sixteen 32k byte FLASH ROM banks (0 to 15) or any of the sixteen 32k byte RAM banks (16 to 31) can be mapped to the bottom 32k bytes of the Z80’s memory space (0x0000 to 0x7FFF) with a single write to I/O address 0x78 (or 0x79). The value written to this I/O address is two times the bank number. Bits 0, 6 and 7 are ignored. This scheme has been used for compatibility with existing software.

Input/output port functions
I/O Address ReadWrite
(0x78 to 0x79)
n/aMemory bank select
Bits 1 to 5 = Bank number (x2)
Bit 5 = RAM (hi), FLASH (lo)
Jumper options
JP1FLASH write enable / protect
Read only = Write protected
Write = Read and write enabled

It is recommended that a jumper shunt be fitted in the “Read only” position of JP1 during normal use. It only needs to be in the “Write” position when the contents of the FLASH is to be updated. While the FLASH device requires a very specific sequence of events to protect it against accidental modification, it is best to play safe and use the jumper to ensure it can not be written to.

Assembly Guide

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

  1. Decoupling capacitors C1 to C6
    These can be fitted either way around
  2. Sockets for U1 to U6
    Fit such that the notch in the socket matches the curve in the outline on the PCB silkscreen
  3. 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
  4. Header pins JP1
  5. 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
  6. Fit the nylon spacer in the mounting hole

Fit a jumper shunt in the position shown below.


  • 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.
  • RomWBW is copyright Wayne Warthen and has been provided free of charge with his permission.

Homebrew 8-bit retro computing