SC791 is a modular Z80 computer designed to run RomWBW and CP/M.
- SC791 – Assembly guide
- SC791 – Compatibility
- SC791 – Firmware, RomWBW RCZ80_std
- SC791 – Firmware, SCM S7
- SC791 – Parts list
- SC791 – User guide
- SC700 series information
- SC700 series support
Downloads
See individual product pages for downloads, such as kit contents sheets, schematics, PCB design files and PCB Gerber files.
Errata
See notes about the Compact Flash adapter.
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
SC791 is made up of the following backplane and modules:
- SC701 – Backplane, 6 vertical sockets, 1 horizontal socket
- SC706 – Z80 CPU module, 7.3728 MHz
- SC714 – Z80 memory module, 512kB RAM, 512kB ROM
- SC716 – Z80 SIO/2 dual serial module
- SC715 – Compact Flash module
Backplane and power options:
- SC701 – Backplane, 6 vertical sockets, 1 horizontal socket, 5 volt power input
- SC702 – Backplane, 6 vertical sockets, 1 horizontal socket plus SC703 – Power supply (8 to 12 volt input) and reset module
- SC709 – Backplane, 12 vertical sockets, 1 horizontal socket, 5 volt power input
- SC710 – Backplane, 12 vertical sockets, 1 horizontal socket plus SC703 – Power supply (8 to 12 volt input) and reset module
A Compact Flash card is also required for file storage. It is not necessary for basic operation.
Once built this system contains:
- Z80 processor
- 512k bytes RAM
- 512k bytes FLASH
- 7.3728 MHz clock
- Voltage supervisor and reset
- Two asynchronous serial ports
- Backplane with power input
Recommended accessories:
- SC346 – Serial to USB C adapter
- SC719 – Digital I/O module
- SC703 – Power supply module, 8 to 15 volt input
A digital I/O module is recommended as it provides LEDs that display diagnostic information as startup and disk activity. It is also useful for general I/O and and an easy way to add debug status during software development.
A digital I/O module is recommended as it provides LEDs that display diagnostic information as startup and disk activity. It is also useful for general I/O and and an easy way to add debug status during software development.
Variations to the base system
The suggested backplane has 6 vertical slots and 1 horizontal slot, plus 5 volt power input and a voltage supervisor and reset device. Alternatives to this set up include different size backplanes and the option of a dedicated power supply and reset module.
- SC701 – RCBus-80pin backplane, 6+1 slots, 5 volt power input
- SC702 – RCBus-80pin backplane, 6+1 slots, extension pins
- SC709 – RCBus-80pin backplane, 12+1 slots, 5 volt power input
- SC710 – RCBus-80pin backplane, 12+1 slots, extension pins
- SC703 – RCBus-80pin, power and reset module, 8 to 15 volts input
- SC712 – RCBus-80pin, power and reset module, 5 volts input
Optional modules
This system can be enhanced with additional modules, such as:
- SC704 – I2C bus master module
- SC711 – Prototyping module
- SC716 – Z80 SIO/2 dual serial port module
- SC717 – Z80 PIO parallel input/output module
- SC718 – Z80 CTC counter/timer module
- SC724 – Breakout module
- SC727 – Real time clock module
Many of the modules designed for the standard 40-pin bus and the 60-pin enhanced bus can also be used with this system. See Compatibility below.
User Guide
The standard distribution of RomWBW assumes a terminal (or computer running terminal software) is connected to serial port A. Typically, this is achieved with a USB to serial adapter (the small PCB shown below) connected to the computer with a USB C cable.
The default serial port settings are: 115200 baud, 8 data, 1 stop, no parity, RTS/CTS hardware no flow control.
A brief guide to using RomWBW can be found here.
Assembly Guide
Build the backplane and modules as described on each product page.
- Backplane: SC701, SC702, SC709 or SC710
- SC703 – Power supply module, 8 to 15 volt input (optional)
- SC706 – Z80 CPU module, 7.3728 MHz
- SC714 – Z80 memory module, 512kB RAM, 512kB ROM
- SC716 – Z80 SIO/2 dual serial module
- SC715 – Compact Flash module
Fit jumper shunts to all header pins as illustrated below
Test the optinal power supply module SC703 before connecting it to the backplane. Power the module from an 8 to 15 volt supply. Turn ON with the toggle switch. The green power LED should light. The red reset LED should light for about half a second and then go off. If you have a volt meter, measure the voltage at J3. It should be between 4.75 and 5.25 volts. Turn OFF with the toggle switch.
Fit the power supply module SC703 to one of the slots on the backplane SC710. The modules can be fitted in any slots and in any order. Repeat the above power and voltage tests.
Fit the processor module SC706 and repeat the power test.
Fit the memory module SC714 and repeat the power test.
Fit the serial module SC716 and repeat the power test.
Connect serial port A to a computer running terminal software. Set the terminal software to 115200 baud, 8 data bits, 1 stop bit, no parity. For the first test select no flow control. Switch on. The startup text should appear in the terminal window. The system should respond to key presses. Select RTS/CTS hardware flow control and repeat the test.
Connect the Compact Flash module but without a Compact Flash card fitted. Switch on. The startup text should appear in the terminal window.
Fit a Compact Flash card and switch on. The startup text should appear in the terminal window.
The system is now be complete. Each ‘drive’ on the Compact Flash card needs to be initialised with the CLRDIR command from CP/M. With recent releases of RomWBW you may need to use FDISK80 first.
Compatibility
This system conforms to the RCBus specification v1.0 for RCBus-Z80 (80-pin).
The backplane conforms fully to the RCBus specification v1.0 and thus supports: RCBus-2014, RCBus-Z80, RCBus-68xx, RCBus-9995.
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 following table indicates electrical compatibility with SC791 with default options. Check firmware and software details for any required software support.
| Product (80-pin) | ? | Compatibility notes |
| SC126 Z180 motherboard |  | Function conflict |
| SC701 Backplane 6+1 | | No male header pins for expansion |
| SC702 Backplane 6+1 |  | Adds 6 module sockets RCBus 80-pin |
| SC703 Power from 12v | | Function conflict SC703 included |
| 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 | | Function conflict SC706 included |
| SC707 Memory 128k | | Function conflict |
| SC708 Z80 SBC | | Function conflict |
| SC709 Backplane 12+1 | | No male header pins for expansion |
| 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 | | Function conflict SC714 included |
| SC715 Compact flash | | Function conflict SC715 included |
| 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 | | Function conflict |
| SC722 Z180 CPU | | Function conflict |
| SC723 Backplane 3 | | No male header pins for expansion |
| 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 | | Function conflict |
| SC792 Z180 system | | Function conflict |
| Product (40 pin) | ? | Compatibility notes |
| SC114 Z80 motherboard | | Function conflict |
| SC130 Z180 motherboard | | Function conflict |
| SC133 Backplane 11+1 | | No male header pins for expansion |
| 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 | | Function conflict |
| SC145 Compact flash | | Function conflict |
| SC147 Backplane 6+1 | | Adds 6 module sockets RCBus 40-pin |
| SC148 Power from 5v | | Function conflict |
| SC149 Z80 CPU | | Function conflict |
| SC150 Paged RAM 128k | | Function conflict |
| SC151 Paged ROM 128k | | Function conflict |
| Other suppliers | ? | Compatibility notes |
| RC2014 Mini system | | Function conflict |
| RC2014 Pro system | | Function conflict |
| RC2014 Zed system | | Function conflict |
| RC2014 Micro module | | Function conflict |
| 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 | | Function conflict |
| RC2014 SIO/2 dual serial | | Function conflict Address conflict |
| RC2014 Compact flash | | Function conflict |
| RC2014 Dual clock | | Generates CLK and CLK2 bus signals |
| RC2014 Pageable ROM | | Function conflict |
| RC2014 64k RAM | | Function conflict |
| RC2014 Memory 512k | | Function conflict |
| 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.
- RomWBW is copyright Wayne Warthen and has been provided free of charge with his permission.
- The Compact Flash interface circuit has been designed by Tadeusz Pycio and reproduced with his permission.
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