SC739 is a USB storage module. It allows RCBus computers to use USB memory stick (also known as thumb drives) for file storage. This module is supported by RomWBW 3.4 and later.

• SC739 – Assembly guide
• SC739 – Compatibility
• SC739 – Parts list
• SC739 – Printed circuit board
• SC739 – User guide
• SC700 series information
• SC700 series support

Downloads

• SC739, v1.0, Kit contents sheet (PDF)
• SC739, v1.0, Schematic (PDF)
• SC739, v1.0, PCB design files (OSHWLab)
• SC739, v1.0, Gerber files (ZIP)

Errata

• Nothing known

Suppliers

Kits	Website	From	Currency
Small Computers Direct	SCDirect	UK	GBP
PCBs	Website	From	Currency
Small Computers Direct	SCDirect	UK	GBP
Assembled and Tested	Website	From	Currency
Not available
Components
See parts list

Parts List

Reference	Qty	Component
PCB	1	SC739, v1.0, PCB
C1 to C4	4	Capacitor, ceramic, 100 nF
C5	1	Capacitor, electrolytic, 1 uF
JP1	1	Header, male, 2 row x 8 pin, angled
JP2	1	Header, male, 1 row x 2 pin, straight
Jumper	8	Jumper shunt
M1	1	CH375 or CH376 USB interface module
P1	1	Header, male, 2 row x 40 pin, angled
R1	1	Resistor, 1k, 0.25W
R2	1	Resistor, 1M, 0.25W
RN1	1	Resistor network, 8x100k, SIL, 9-pin
S1	1	Socket, 2 row x 8 pin, straight Optional for mounting CH375/6
S2 and S3	2	Socket, 1 row x 3 pin, straight Optional for mounting CH375/6
Screw for spacer	1	Machine screw, 6mm, M3
Screws for standoffs	4	Machine screw, M2 x 6 mm Optional for mounting CH375/6
Spacer	1	Spacer, 10mm, M3, nylon
Standoffs	2	Standoff, M2 x 11 mm, brass Optional for mounting CH375/6
U1	1	74HCT688
U2	1	74HCT125
IC socket 20-pin U1	1	Socket, DIP, 20-pin
IC socket 14-pin U2	1	Socket, DIP, 14-pin

Printed Circuit Board

User Guide

SC739 is a module dedicated to generating a system reset signal.

The system reset signal is generated at power up, upon pressing switch SW1, or with an external switch connected to P2. The power up reset is generated by the voltage supervisor U5. The supervisor will also hold the system in reset if the 5-volt supply drops below about 4.75 volts. In addition, the supervisor cleans up the reset signal generated with the reset button.

A hardware reset can also be generated by writing to the I/O port address selected with JP1. The suggested address is 47 hexadecimal (71 decimal). The value written to the port is irrelevant, any value will work. A clean reset signal is generated that lasts 128 clock cycles, typically approximately 17 microseconds.

To initiate a hardware reset from an assembler program:
OUT ($47), A

To initiate a hardware reset from SCM, enter the command:
O 47 0

To initiate a hardware reset from BASIC, enter the command:
OUT 71, 0

The system should only have one enabled voltage supervisor. If there is another one in the system, one of them needs to be disabled. The circuit on this module is likely to be the best one, so ideally keep this one enabled and disable any others. To enable the supervisor on this module, fit a jumper shunt to header pins JP2.

Input/output port functions

RCBus I/O Address	Read/Write
Configurable *1	Access CH375/6 interface module

1. The RCBus I/O base address should be set to match the software you are using. Typically, this is 0x3E (jumper shunts fitted for bits 1, 2, 3, 4, 5).

Jumper options

Jumper	Function
JP1	Set module’s RCBus I/O address The default is: 0x3E (first CH375/6 module) 0x3C (second CH375/6 module)
JP2	Connect interrupt output to RCBus Typically, leave disconnected

Connectors

Connector	Function
P 1	RCBus connector
S1, S2, S3	Optional sockets for CH375/6 module

Assembly Guide

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

1. Resistors R1 (1k), R2 (1M)
   These can be fitted either way around
2. Decoupling capacitors C1 to C4 (100 nF)
   These can be fitted either way around
3. Capacitor C5 (100 uF)
   This must be fitted the correct way around, as described here
4. Sockets for U1 to U2
   Fit such that the notch in the socket matches the curve in the outline on the PCB silkscreen
5. Resistor network RN1 (8 x 100k)
   These must be fitted the correct way around whereby the dot on the component matches the dot on the PCB silkscreen
6. 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
7. Header pins JP1 (2 row x 8 pin, angled)
8. Header pins JP2 (1 row x 2 pin, straight)
9. LED1
   The angled LEDs in the kit only fit one way around, but standard LEDs need to have the short lead in the hole marked with a flat line
10. Optional sockets for the CH375/6 USB interface module
    The USB module can be socketed or solders directly. Sockets result in the module being too ‘wide’ to use with another module in the next backplane socket.
    Fit S1 (2 row x 8 pin, straight, socket)
    Fit S2 (1 row x 3 pin, straight, socket)
    Fit S3 (1 row x 3 pin, straight, socket)
    Fit CH375/6 USB interface with standoffs and screws
    Alternatively, solder the CH375/6 USB interface module
11. 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
12. Fit the nylon spacer in the mounting hole

Fit jumper shunts in the positions shown below. All other jumpers are optional and should only be fitted if the feature is required.

Compatibility

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

The RCBus specification includes RCBus-2014 (both RC2014 standard 40-pin bus and RC2014 enhanced 60-pin bus) and also the full 80-pin RCBus. The 80-pin RCBus provides support for advanced Z80 features, such as the interrupt daisy-chain, as well as support for other processor families.

Backplane	?	Compatibility notes
RCBus 80-pin		Fully supported
RCBus 60-pin (RC2014 enhanced)		Fully supported
RCBus 40-pin (RC2014 standard)		Fully supported

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.