SC703 is a power supply module for RCBus.
- SC703 – Assembly guide
- SC703 – Compatibility
- SC703 – Parts list
- SC703 – Printed circuit board
- SC703 – User guide
- SC700 series information
- SC700 series support
Downloads
- SC703, v1.1, Kit contents sheet (PDF)
- SC703, v1.1, Schematic (PDF)
- SC703, v1.1, PCB design files (OSHWLab)
- SC703, v1.1, 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 | SC703, v1.0, PCB |
| C1 and C2 | 2 | Capacitor, electrolytic 100 µF |
| C3 and C4 | 2 | Capacitor, ceramic, 100 nF |
| C5 | 1 | Capacitor, ceramic, 1 nF |
| D1 | 1 | Diode, 1N4001 |
| J1 | 1 | Socket, power, barrel, 2.1mm |
| J2 and J3 | 2 | Screw terminal, 2 way, 5mm pitch |
| JP1, P2, P3 | 3 | Header, male, 1 row x 2 pin, angled or 8 pin strip with 2 pins removed |
| JP2 | 1 | Wire link (eg. resistor offcut), or Header, male, 1 row x 3 pin, straight |
| Jumper | 2 | Jumper shunt |
| LED1 | 1 | LED, green, 3mm, angled |
| LED2 | 1 | LED, red, 3mm, angled |
| P1 | 1 | Header, male, 2 row x 40 pin, angled |
| P2 and P3 | see JP1 | |
| R1 and R2 | 2 | Resistor, 1k, 0.25W |
| R3 | 1 | Resistor, 100k, 0.25W |
| R4 | 1 | Resistor, 10k, 0.25W |
| R5 and R6 | 2 | Resistor, 4k7, 0.25W |
| SW1 | 1 | Switch, toggle, sub-miniature, SPDT |
| SW2 | 1 | Switch, tactile button, angled |
| Screw (for spacer) | 1 | Machine screw, 6mm, M3 |
| Spacer | 1 | Spacer, 10mm, M3, nylon |
| Nut (for U1) | 1 | Nut, M3.5 |
| Bold (for U1) | 1 | Bolt, M3.5, 10mm, pan head |
| Heatsink (for U1) | 1 | Heatsink TO-220, 19x20x9mm |
| U1 | 1 | 7805 regulator, 5V, 1A |
| U2 | 1 | DS1233-5+ supervisor |
| U3 | 1 | 74HCT125 |
| IC socket 14-pin U3 | 1 | 14-pin PDIP socket |
Printed Circuit Board
User Guide
This module provides a regulated 5-volt supply to the backplane. Voltage input is between 8 and 15 volts D.C. at a maximum of 1 ampere. The regulator will get warm in normal use. The higher the input voltage and the greater the current load, the hotter it will get. The input can be connected to either J1 (centre positive) or the screw terminal J2.
The 5-volt output is connected to the backplane and is also available at screw terminal J3 and header pins P3.
The system reset signal is generated at power up, upon pressing switch SW2, or with an external switch connected to P2. The power up reset is generated by the voltage supervisor U2. 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.
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 JP1.
Input/output port functions
| RCBus I/O Address | Read | Write |
| none | n/a | n/a |
Jumper options
| Jumper | Function |
| JP 1 | Enable the voltage supervisor Only one supervisor should be enabled in a system so it may be necessary to disable (isolate) one of them |
| JP 2 | Select the polarity of the on/off switch, either UP for ON or DOWN for ON |
Connectors
| Connector | Function |
| J 1 | Barrel socket, power supply input, 8 to 15 volts D.C. centre positive, maximum current 1 ampere |
| J 2 | Screw terminal, power supply input, 8 to 15 volts D.C. centre positive, maximum current 1 ampere |
| J 3 | Screw terminal, 5-volt output, maximum current 1 ampere |
| P 1 | RCBus connector |
| P 2 | Header pins, optional external reset switch |
| P 3 | Header pins, 5-volt output, maximum current 1 ampere |
Assembly Guide
Below is the suggested order of assembly. A general guide to assembling circuit boards can be found here.
- Resistors R1 to R6
These can be fitted either way around - Diode D1
This must be fitted the correct way around, with the band on the diode matching the marking on the PCB - Socket for U3
Ensure the notch in the socket matches the marking on the PCB - Header pins P1
- Capacitor C5
This can be fitted either way around - Capacitors C3 and C4
These can be fitted either way around - Capacitors C1 and C2
This must be fitted the correct way around, as described here - Switch SW1
- LED1 and LED2
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, as described here - Switch SW2
- Header pins JP1, P2 and P3
P2, JP1 and P3 can be a single strip with two pins removed - Barrel power socket J1
- Screw terminals J2 and J3
- Regulator U1 and heatsink
- Header pins JP2
- Voltage supervisor U2
Carefully bend the legs to match the hole spacing on the PCB and ensure the orientation matches the markings on the PCB - Fit IC’s U3 into its socket
Ensure the notch in the IC matches the PCB and IC socket - Fit jumper shunts to JP1 and JP2
JP2 has two possible positions depending on your preference for the on/off switch polarity (ie. UP=ON or DOWN=ON) - Fit the nylon spacer in the mounting hole
Compatibility
This module conforms fully to the RCBus specification v1.0 and thus supports: RCBus-2014, RCBus-Z80, RCBus-68xx, RCBus-9995.
It is fully functional on backplanes with 40 or 80 pin sockets.
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 |
The following table indicates electrical compatibility with SC703. Check firmware and software details for any required software support.
| Product (80-pin) | ? | Compatibility notes |
| SC126 Z180 motherboard | | Adds Z180 SBC/ motherboard |
| SC701 Backplane 6+1 | | Adds 6 module sockets RCBus 80-pin and PSU |
| SC702 Backplane 6+1 | | Adds 6 module sockets RCBus 80-pin |
| SC703 Power from 12v |  | Function conflict |
| SC704 I2C bus master | | Adds I2C bus master and I2C EEPROM |
| SC705 Serial ACIA | | Adds one serial port Typically set to 0x40 |
| SC706 Z80 CPU | | Adds Z80 CPU and main bus clock |
| SC707 Memory 128k | | Adds 128k RAM and 128k flash ROM |
| SC708 Z80 SBC | | Adds CPU, ROM, RAM clock and reset |
| SC709 Backplane 12+1 | | Adds 12 module sockets RCBus 80-pin and PSU |
| SC710 Backplane 12+1 | | Adds 12 module sockets RCBus 80-pin |
| SC711 Prototyping | | Prototyping module |
| SC712 Power from 5v | | Function conflict |
| SC713 RCBus tool | n/a | Simple reference tool No electrical function |
| SC714 Memory 512k | | Adds 512k RAM and 512k flash ROM |
| SC715 Compact flash | | Adds Compact Flash storage |
| SC716 Z80 SIO/2 | | Adds two serial ports Typically set to 0x84 |
| SC717 Z80 PIO | | Adds parallel I/O using Z80 PIO |
| SC718 Z80 CTC | | Adds counter/timer using Z80 CTC |
| SC719 Digital I/O | | Adds digital I/O Eight in, eight out |
| SC720 Z80 motherboard | | Function conflict |
| SC721 Memory 512k | | Adds 512k RAM and 2 x 512k flash ROM |
| SC722 Z180 CPU | | Adds Z180 CPU with two serial ports |
| SC723 Backplane 3 | | Adds 3 module sockets RCBus 80-pin |
| SC724 Breakout | | Prototyping breakout module |
| SC725 SIO+CTC | | Adds two serial ports and 4 counter/timers |
| SC726 Clock generator | | Generates CLK and CLK2 bus signals |
| SC727 Real time clock | | Adds real time clock for time and date |
| SC728 Module riser | | Simple module riser for RCBus 80-pin |
| SC791 Z80 system | | Modular Z80 system |
| SC792 Z180 system | | Modular Z180 system |
| Product (40 pin) | ? | Compatibility notes |
| SC114 Z80 motherboard | | Adds Z80 SBC/ motherboard |
| SC130 Z180 motherboard | | Adds Z180 SBC/ motherboard |
| SC133 Backplane 11+1 | | Adds 11 module sockets RCBus 40-pin and PSU |
| SC134 LED output port | | Adds eight LED outputs |
| SC135 Digital output port | | Adds eight digital outputs |
| SC136 Digital input port | | Adds eight digital inputs |
| SC137 I2C bus master | | Adds I2C bus master |
| SC139 Serial ACIA | | Adds one serial port Typically set to 0x40 |
| SC141 Backplane 12+1 | | Adds 12 module sockets RCBus 40-pin |
| SC142 Power from 12v | | Function conflict |
| SC143 Flash ROM | | Adds 128k flash ROM |
| SC145 Compact flash | | Adds Compact Flash storage |
| SC147 Backplane 6+1 | | Adds 6 module sockets RCBus 40-pin |
| SC148 Power from 5v | | Function conflict |
| SC149 Z80 CPU | | Adds Z80 CPU and main bus clock |
| SC150 Paged RAM 128k | | Adds 128k of paged RAM |
| SC151 Paged ROM 128k | | Adds 128k of paged ROM |
| Other suppliers | ? | Compatibility notes |
| RC2014 Mini system | | Adds Z80 SBC/ motherboard |
| RC2014 Pro system | | Modular Z80 system |
| RC2014 Zed system | | Modular Z80 system |
| RC2014 Micro module | | Adds CPU, ROM, RAM serial, clock and reset |
| RC2014 Backplane 5 | | If header pins fitted it adds 4 x 40-pin sockets |
| RC2014 Backplane 8 | | No male header pins for expansion |
| RC2014 Backplane Pro | | No male header pins for expansion |
| RC2014 Z80 CPU | | Adds Z80 CPU |
| RC2014 SIO/2 dual serial | | Adds two serial ports at 0x80 to 0x87 |
| RC2014 Compact flash | | Adds Compact Flash at 0x10 to 0x17 |
| RC2014 Dual clock | | Generates CLK and CLK2 bus signals |
| RC2014 Pageable ROM | | Adds 64k paged ROM |
| RC2014 64k RAM | | Adds 64k paged RAM |
| RC2014 Memory 512k | | Adds 512k RAM and 512k flash ROM |
| RC2014 Digital I/O | | Adds eight LED outputs and eight push buttons |
| RC2014 Real time clock | | Adds real time clock for time and date |
| RC2014 RP2040 VGA terminal | | Connect VGA monitor and USB keyboard |
| RC2014 Pi Pico terminal | | Connect VGA monitor and USB keyboard |
| RC2014 YM2149 sound card | | Adds authentic retro sound |
| Weird electronics Flock v2 | | Adds floppy disk and real time clock |
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 