SC707 – RCBus Z80 Memory Module

SC707 is a memory module with 128k bytes of FLASH ROM and 128k pages of RAM designed for the RCBus. This module provides suitable memory for running 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

PCB1SC707, v1.0, PCB
C1 to C44Capacitor, ceramic, 100 nF
JP1+2+31Header, male, 2 row x 10 pin, angled
Jumper3Jumper shunt
LED1 and 22LED, green, 3mm, angled
P11Header, male, 2 row x 40 pin, angled
R1 and R22Resistor, 1k, 0.25W
Screw (for spacer)1Machine screw, 6mm, M3
Spacer1Spacer, 10mm, M3, nylon
U11FLASH 128k bytes SST39SF010A
U21RAM 128k bytes AS6C1008
IC socket 32-pin
U1 and U2
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

SC707 provides 128k of banked FLASH ROM and 128k bytes of RAM, together with paging control of the lower 32k. This configuration is suitable to run CP/M 2.

At reset the output bits of integrated circuit U4 are all cleared to zero (low voltage). The ROM is paged into memory from 0x0000 to 0x7FFF (32k bytes) with RAM from 0x8000 to 0xFFFF (32k bytes). When input/output address 0x38 bit 0 is set to one (a high voltage) the ROM is paged out and RAM is paged in, giving a full 64k bytes of RAM from 0x0000 to 0xFFFF.

The 128k bytes of FLASH ROM is split into four 32k byte banks. The bank is selected with JP2 (FLASH address A15) and JP3 (FLASH address A16). By default these jumpers should be set to ‘0’ selecting the lowest 32k bytes. By setting jumpers to either 0 or 1, any of the four banks can be selected. Alternatively, these jumpers can be set for software selection of the bank, using output addresses 0x20 bit 0 and 0x28 bit 0.

The 128k bytes of RAM is split into two 64k byte banks. The bank can be selected with output addresses 0x30 bit 0

The status LED should be ON when the system is in reset. With the recommended firmware, the LED should flash OFF for about half a second when the system is released from reset. It should then turn ON and stay on. User software can then control the LED, as required.

Input/output port functions
I/O Address ReadWrite
(0x00 to 0x03)
n/aUser LED (LED 2)
Low = OFF, high = ON
(0x08 to 0x0B)
n/aStatus LED (LED 1)
Low = ON, high = OFF
(0x20 to 0x23)
n/aROM bank select
(0x28 to 0x2B)
n/aROM bank select
(0x30 to 0x33)
n/aRAM bank select
(0x38 to 0x3B)
n/aMemory paging (lower 32k)
Low = ROM, high = RAM
Jumper options
JP1FLASH write enable / protect
Read only = Write protected
Write = Read and write enabled
JP2FLASH bank select
JP2.1 = FLASH A15 high
JP2.2 = Software select FLASH A15 via port 0x20
JP2.3 = FLASH A15 low
JP3FLASH bank select
JP3.1 = FLASH A16 high
JP3.2 = Software select FLASH A16 via port 0x28
JP3.3 = FLASH A16 low

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. Resistors R1 and R2
    These can be fitted either way around
  2. Sockets for U1, U2 and U3
    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. Decoupling capacitors C1, C2, C3 and C4
    These can be fitted either way around
  5. Light emitting diodes LED1 and LED2
    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
  6. Header pins JP1, JP2 and JP3
    This can be one header with a few pins pulled out or three separate headers. Fit a jumper shunts in the “Read only” position of JP1 and in position “0” of JP2 and JP3
  7. 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
  8. 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.

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