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.

• SC714 – Assembly guide
• SC714 – Compatibility
• SC714 – Firmware, RomWBW
• SC714 – Firmware, SCM
• SC714 – Parts list
• SC714 – Printed circuit board
• SC714 – User guide
• Designing your RCBus computer
• SC700 series information
• SC700 series support

Downloads

• SC714, v1.0, Kit contents sheet (PDF)
• SC714, v1.0, Schematic (PDF)
• SC714, v1.0, PCB design files (OSHWLab)
• SC714, v1.0, Gerber files (ZIP)

Errata

Nothing known

Suppliers

Kits	Website	Ships from
Stephen C Cousins	Tindie	UK
PCBs	Website	Ships from
Stephen C Cousins	Tindie	UK
Assembled and Tested	Website	Ships from
Not available
Components
See parts list

Parts List

Reference	Qty	Component
PCB	1	SC714, v1.0, PCB
C1 to C6	6	Capacitor, ceramic, 100 nF
JP1	1	Header, male, 1 row x 3 pin, angled
Jumper	1	Jumper shunt
P1	1	Header, male, 2 row x 40 pin, angled
Screw (for spacer)	1	Machine screw, 6mm, M3
Spacer	1	Spacer, 10mm, M3, nylon
U1	1	FLASH 512k bytes SST39SF040
U2	1	RAM 512k bytes AS6C4008
U3	1	74HCT688
U4	1	74HCT273
U5	1	74HCT157
U6	1	74AHCT139
IC socket 32-pin U1 and U2	2	Socket, DIP, 32-pin
IC socket 20-pin U3 and U4	2	Socket, DIP, 20-pin
IC socket 16-pin U5 and U6	2	Socket, DIP, 16-pin

Printed Circuit Board

Compatibility

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	Read	Write
0x78 (0x78 to 0x79)	n/a	Memory bank select Bits 1 to 5 = Bank number (x2) Bit 5 = RAM (hi), FLASH (lo)

Jumper options

Jumper	Function
JP1	FLASH 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.

Notes

• 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.