Version 2.0 adds a serial port and updates Monitor to Save and Load SREC

A project log for Nanocomp 6809 8 Bit Retro Computer on Breadboards

Wireless World Magazine in January and June 1981 published this design. Reproduced on solderless breadboards using the original Monitor ROM

dave-henryDave Henry 11/03/2022 at 00:370 Comments

Version 1.0 of the Nanocomp 6809 re-produced the same design as the 1981 version so the original Monitor ROM could be used unchanged. The Cassette interface electronics was not re-produced as this would be obsolete with the introduction of a serial port connected to a modern PC over USB.

Version 2.0 of Nanocomp is possible as the original Monitor ROM has been disassembled in video 12 in the Nanocomp 6809 Playlist so that enhancements can be made to support a serial port.

The Motorola MC6850 is used to provide a serial port, with a dedicated clock with frequencies designed to divide down to common Baud rates (9600 Baud, 8 Bits, No Parity is used). Rather than using the RS232 serial standard which requires +/- 12V signals, a TTL to Serial USB adaptor is used to interface the MC6850 to the PC. The RealTerm terminal emulator is the used to test the serial ports and for loading and saving SREC program files.

Further developments are planned. Exact Version numbers may change.

Version 3 will add Data, Address and Control line buffer chips to allow expansion of the Nanocomp beyond the 4 LS TTL loads the 6809 supports. This will also expand the address space used from 32KB (A15 was not used in the original Nanocomp) to 64KB and the accessible RAM will be expanded from 4KB to 32KB. The full 8KB of the EEPROM will also be usable.

Version 4 will add a VGA compatible video card capable of 640x480 Text and basic graphics in 16 colours running on breadboards.

Version 5 will try and implement some form of Tetris type game (though without sound), so the response to "Does it run Tetris" can be yes! This spec of hardware will never be able to run Doom!

The documents, datasheets, ROM binaries, source and other files are all maintained in Github

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