SC151 – Paged ROM Module (RC2014)

SC151 is a 128k byte paged FLASH ROM module designed for the RC2014 bus. It is primarily intended to be used with the paged RAM module (SC150). Together these modules provide suitable memory for running CP/M.



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

Parts List

PCB1SC151, v1.0, PCB
C1 to C33Capacitor, ceramic, 100 nF
JP11Header, male, 1 row x 3 pin, straight
Jumper1Jumper shunt
LED11LED, blue, 3mm
P11Header, male, 1 row x 40 pin, angled
R11Resistor, 1k, 0.25W
U31SST39SF010A (128k byte FLASH)
U1 socket1Socket, DIP, 14-pin
U2 socket1Socket, DIP, 16-pin
U3 socket1Socket, DIP, 32-pin

Printed Circuit Board

User Guide

SC151 provides 128k of banked FLASH ROM together with paging control of the lower 32k. SC150 provides the matching RAM. Together they provide suitable memory for CP/M.

At reset the output bits of integrated circuit U2 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.

This module contains 128k bytes of FLASH ROM, split into four 32k byte banks. The banks can be select with output addresses 0x20 bit 0 and 0x28 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
(0x08 to 0x0B)
n/aStatus LED
Low = ON, high = OFF
(0x20 to 0x23)
n/aROM bank select
(0x28 to 0x2B)
n/aROM bank select
(0x38 to 0x3B)
n/aMemory paging (lower 32k)
Low = ROM, high = RAM
Jumper options
JP1FLASH write protect
RD = Read only (write protected)
WR = Read and write enabled

It is recommended that a jumper shunt be fitted in the RD position of JP1 during normal use. It only needs to be in the WR 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.

  • Resistor R1 (1k)
    This can be fitted either way around
  • Sockets for U1, U2 and U3
    Fit such that the notch in the socket matches the curve in the outline on the PCB silkscreen
  • 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
  • Decoupling capacitors C1, C2 and C3
    These can be fitted either way around
  • 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
  • Header pins JP1
    Fit a jumper shunt in the RD position
  • 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


  • 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.
  • The product contains small parts and is not suitable for young children.

Homebrew 8-bit retro computing