SC734 is a micro SD card storage module for the 80-pin RCBus.
See user guide (below) for details of support in RomWBW.
- SC734 – Assembly guide
- SC734 – Compatibility
- SC734 – Parts list
- SC734 – Printed circuit board
- SC734 – User guide
- SC700 series information
- SC700 series support
Downloads
- SC734, v1.0, Kit contents sheet (PDF)
- SC734, v1.0, Schematic (PDF)
- SC734, v1.0, PCB design files (OSHWLab)
- SC734, v1.0, Gerber files (ZIP)
Errata
Nothing known
Suppliers
| Kits | Website | From | Currency |
| Small Computers Direct | SCDirect | UK | GBP |
| Stephen C Cousins | Tindie | UK | USD |
| Small Computer Central | Lectronz | UK | Euro/USD |
| PCBs | Website | From | Currency |
| Small Computers Direct | SCDirect | UK | GBP |
| Stephen C Cousins | Tindie | UK | USD |
| Small Computer Central | Lectronz | UK | Euro/USD |
| Assembled and Tested | Website | From | Currency |
| Not available | |||
| Components | |||
| See parts list |
Tindie does not collect VAT for EU countries
Lectronz does collect EU VAT for orders up to 150 EUR
Parts List
| Reference | Qty | Component |
| PCB | 1 | SC734, v1.0, PCB |
| C1 to C3 | 3 | Capacitor, ceramic, 100 nF |
| C4 | 1 | Capacitor, electrolytic, 100 µF |
| JP1 | 1 | Header, male, 2 row x 8 pin, angled |
| Jumper | 8 | Jumper shunt |
| P1 | 1 | Header, male, 2 row x 40 pin, angled |
| P2 | 1 | Header, male, 1 row x 8 pin, angled |
| P3 | 1 | Header, male, 1 row x 6 pin, angled |
| R1 to R4 | 4 | Resistor, 10k, 0.25W |
| RN1 | 1 | Resistor network, 8x100k, SIL, 9-pin |
| S1 | 1 | Header, female, 1 row x 6 pin, angled |
| Screw (for spacer) | 1 | Machine screw, 6mm, M3 |
| Spacer | 1 | Spacer, 10mm, M3, nylon |
| Adapter | 1 | MicroSD card adapter |
| U1 | 1 | 74HCT688 |
| U2 | 1 | 74HCT273 |
| U3 | 1 | 74HCT125 |
| IC socket 20-pin U1 and U2 | 2 | Socket, DIP, 20-pin |
| IC socket 14-pin U3 | 1 | Socket, DIP, 14-pin |
Printed Circuit Board
Note: The PCB is designed to allow a DIP switch to be fitted instead of the header pins JP1.
User Guide
SC734 is an SD card storage module for the 80-pin RCBus.
Support is included in RomWBW v3.5 but not in the Small Computer Monitor (SCM).
To enable support in RomWBW v3.4 the following line needs to be added to the RCBus_std configuration file:
SDENABLE .SET TRUE ; SD: ENABLE SD CARD DISK DRIVER
This module provides simple bit-bang data transfer so it is slow, similar to a 1980 floppy disk but with much greater capacity.
The RCBus I/O port address for this module is set in binary with JP1. Fit a jumper shunt to each bit position where the address bit should be a logic ‘1’ (high voltage).
The address assumed by RomWBW is hexadecimal 69 or binary 01101001. The jumper shunt positions required for this address are illustrated below.
Jumper shunts for RCBus address hexadecimal 69 (or binary 01101001)
Input/output port functions
| RCBus I/O Address | Read | Write |
| Configurable *1 | Read 0: IN0 1: not used 2: not used 3: not used 4: not used 5: not used 6: not used 7: MISO | Write 0: MOSI 1: OUT1 2: OUT2 3: /CS 4: SCK 5: OUT5 6: OUT6 7: OUT7 |
- The RCBus I/O address should be set to match the software you are using. Typically, this is 0x69.
Jumper options
| Jumper | Function |
| JP 1 | Set SC734’s RCBus I/O address |
Assembly Guide
Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.
- Resistors R1 to R4 (10k)
- Header socket S1 (1 row x 6 way, angled)
- Decoupling capacitors C1 to C3 (100 nF)
These can be fitted either way around - Bus header pins P1 (1 row x 40 way, angled)
- Header pins P2 (1 row x 8 way, angled)
- Header pins P3 (1 row x 6 way, angled)
- IC sockets for U1 to U3
Ensure the notch in the socket matches the marking on the PCB - 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 - Jumper pins JP1 (2 row x 8 pin, angled)
- Fit the IC’s in their sockets
Ensure the notch in the IC matches the PCB and IC socket - Capacitor C4 (100 uF)
This must be fitted the correct way around, as described here - Fit the nylon spacer in the mounting hole
- Fit the Micro SD card adapter to socket S1
You may need to bend the adapter’s header pins a little to make the adapter sit parallel to the SC734 PCB
Fit jumper shunts in the positions shown below.
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.
The table below indicates electrical compatibility with each backplane type (40, 60 and 80 pin)
| 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.
Small Computer Central 