SC612 is a serial port module for the 40-pin RCBus.
A comparison of serial modules can be found here.
- SC612 – Assembly guide
- SC612 – Compatibility
- SC612 – Parts list
- SC612 – Printed circuit board
- SC612 – User guide
- SC600 series information
- SC600 series support
Downloads
- SC612, v1.0, Kit contents sheet (PDF)
- SC612, v1.0, Schematic (PDF)
- SC612, v1.0, PCB design files (OSHWLab)
- SC612, 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 | SC612, v1.0, PCB |
| C1 to C5 | 5 | Capacitor, ceramic, 100 nF |
| C6 and C7 | 2 | Capacitor, ceramic, 22 pF |
| JP1+JP2+JP3 +P2 | 1 | Header, male, 1 row x 14 pin, angled Some pins need to be removed |
| JP4 | 1 | Header, male, 1 row x 3 pin, straight |
| JP5 | 1 | Header, male, 2 row x 8 pin, straight |
| Jumper | 5 | Jumper shunt |
| P1 | 1 | Header, male, 1 row x 40 pin, angled |
| P2 | – | see JP1 (above) |
| R1 to R4 | 4 | Resistor, 2k2, 0.25W |
| R5 and R6 | 2 | Resistor, 100k, 0.25W |
| R7 | 1 | Resistor, 1k, 0.25W |
| R8 | 1 | Resistor, 1M, 0.25W |
| S1 | 1 | Header, female, 1 row x 6 pin, angled |
| Screw (for spacer) | 1 | Machine screw, 6mm, M3 |
| Spacer | 1 | Spacer, 10mm, M3, nylon |
| U1 | 1 | 68B50 ACIA |
| U2 | 1 | 74HCT138 |
| U3 | 1 | 74HCT74 |
| U4 | 1 | 74HCT02 |
| U5 | 1 | 74HCT393 |
| X1 | 1 | Crystal, 7.3728 MHz |
| IC socket 24-pin U1 | 1 | Socket, DIP, 24-pin |
| IC socket 16-pin U2 | 1 | Socket, DIP, 16-pin |
| IC socket 14-pin U3, U4, U5 | 3 | Socket, DIP, 14-pin |
Printed Circuit Board
User Guide
The serial port provides bidirectional asynchronous serial communications usually at 115200 baud, 8 data bits, 1 stop bit, no parity. RTS/CTS handshaking provides hardware flow control in both directions. The interface is at 5-volt (TTL) levels.
The default address is 128 decimal, which is 0x80 in hexadecimal and 1000000 in binary. To set this as the address requires a jumper shunt to be fitted to JP4 in the position illustrated below. The module occupies two I/O addresses, either 0x80 & 0x81 or 0x40 & 0x41.
The baud rate is set with a single jumper shunt on JP5. Typically, the rate is 115200 baud, as illustrated below. The available options are 2400, 4800, 9600, 14400, 19200, 38400, 57600 and 115200. These baud rates assume the software sets the ACIA’s internal divider to 64. As the baud rate is set in hardware, the software may not be aware of the actual baud rate and might indicate, for example, that it is running at 115200 baud when it is actually set to, say, 9600 baud.
Jumper JP1 connects the module’s 5-volt supply to the serial port. A jumper should should be fitted here if the RCBus system is being powered from this serial port or if the device connected to this serial port needs to be powered from the RCBus system.
JP2 and JP3 enable the ACIA’s RXD and TXD signals to be connected to the RCBus RX and TX pins as illustrated below.
Input/output port functions
| RCBus I/O Address | Read | Write |
| Configurable *1 | Read ACIA | Write ACIA |
| base + 0 | Status register | Control register |
| base + 1 | Receive data register | Transmit data register |
- The RCBus I/O address should be set to match the software you are using, either 0x80 or 0x40.
Jumper options
| Jumper | Function |
| JP 1 | Connects 5-volt power to serial port |
| JP 2 | Connects the transmit data signal from the ACIA to pin 35 of the RCBus |
| JP 3 | Connects the receive data signal to the ACIA from pin 36 or the RCBus |
| JP 4 | Set SC612’s RCBus I/O address, either 80 or 40 The default is 80 (hexadaecimal) |
| JP 5 | Sets the baud rate The default is 115200 baud |
Assembly Guide
Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.
- Resistors R1 to R8
These can be fitted either way around - Socket S1
Ensure this is fitted flat against the PCB - Decoupling capacitors C1 to C5 (100 nF)
These can be fitted either way around - Bus header pins P1
- Header pins JP1+JP2+JP3+P2
Fit as one strip with pins 5 and 12 removed - Crystal X1
- IC sockets for U1 to U5
Ensure the notch in the socket matches the marking on the PCB - Capacitors C5 and C6 (22 pF)
These can be fitted either way around - Header pins JP4 and JP5
- Fit the IC’s in their sockets
Ensure the notch in the IC matches the PCB and IC socket - Fit the nylon spacer in the mounting hole
Fit jumper shunts in the positions shown below.
Compatibility
This module conforms to the RCBus specification v1.0 for RCBus-2014 (40-pin bus) and RCBus-Z80 (40-pin bus).
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 |
RomWBW includes support for this module, as does the Small Computer Monitor.
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 