The aim of this design is to make entry into the RCBus/RC2014 universe easier and more reliable, by using fewer components, less soldering, fewer configuration jumpers, and fewer circuit boards. 

This motherboard can work in a modest way as a single board computer (SBC), yet can easily be expanded to run CP/M and more.

If you are looking for something a little more advanced, you might like to consider SC126 or SC130.

Features

• Z80 running at 7.3728 MHz
• 128k bytes RAM (second 64k not easy to use, so best consider it to be 64k usable)
• 32k bytes ROM, which can be paged out with the usual write to port 0x38
• Simple bit-bang serial port to get you started
• Four RCBus-2014 40-pin (RC2014 compatible) bus sockets
• Simple reset button (no power-on reset or reset debounce)
• LED for power and status indication
• Runs the Small Computer Monitor, with ROM BASIC and the CP/M loader included
• Comprehensive documentation

The idea is that you can build the board without even fitting those tedious RCBus/RC2014 sockets, then test it with the simple bit-bang serial port. This only involves assembling the components shown in the close-up picture above. That's 5 chips + oscillator + 6 pin header + a few Rs and Cs + LED + reset button.

It looks like this takes about 175 solder joints. This sounds a lot but is way fewer than a typical RCBus/RC2014. There should be a good chance of such a simple circuit working first time. If it doesn't work then it is a relatively simple circuit to troubleshoot. The onboard LED can flash results of the self-test, so a serial port problem will not look like a dead processor.

You can then add the four 40 pin RCBus/RC2014 module sockets. So that's a further 160 solder joints, but it is incremental assembly thus relatively easy to work out where any new fault is.

The next step would be to build and test a proper serial port, such as the official Z80 SIO module. Then, if you want CP/M, all you need to add is the official Compact Flash module and a Compact Flash card with the standard RC2014 CP/M distribution installed. All this is supported by the ROM with no configuration required.

You can even add backplanes from the modular backplane range, although their functionality is limited by the single row standard 40 pin expansion socket on the motherboard.

The motherboard has relatively few components and is thus quite a cheap build, so if it does not prove expandable enough it is not a big deal to discard it, take the useful modules and move to a Pro-style system.

Documentation

This product has a user guide and an assembly guide. The Small Computer Monitor has a user guide and a detailed tutorial. The documentation can be found at www.smallcomputercentral.com

Compatibility

This computer conforms to the RCBus specification v1.0 for RCBus-2014 40-pin systems.

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 Kit

The full kit contains everything you need to build the motherboard, except solder, tools, and cleaning materials. To use the completed motherboard you require a USB to serial adapter (5-volt power and 5-volt signals), a computer, and a terminal program, such as Tera Term. The ROM is supplied programmed with the Small Computer Monitor.

If you have any doubts about sourcing a suitable USB to serial adapter, you might like to include this option with your kit.

Printed Circuit Board

The printed circuit board is available on its own here.

Notes

• This product is supplied as a kit of parts that require assembly.
• It is your responsibility to pay any import duty or taxes charged by your home country.
• This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.
• This product is made in accordance with the "designed for RC2014" labelling scheme.
• RC2014 is a trademark of RFC2795 Ltd.

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