Thursday, 20 October 2011

My NASCOM expansion boards

48K RAM board with EPROMs
EPROM board

Some details of the add-on boards in my NASCOM rack. I mounted the main board in a 19inch rack. A bus was constructed using veroboard. Onto this was mounted multi-pin connectors. There was space for five expansion boards. The boards slotted in from the front. The PSU was wired to the bus and from there to the NASCOM main board. A "buffer" board connected the expansion bus to the NASCOM main bus connector.

In the pictures below you will see the back of the one of the memory boards. This one never worked, due to timing problems. The community suggested various "hacks" involving capacitors, but the board never worked. It sits in the rack unconnected as a 'space' for memory chips. A replacement board had to be bought and built.

The EPROMs you see in the pictures below are:

- A dis-assembler and debugger
- Something called "NASPEN" (cannot remember what this was)
- ZEAP, a popular Z80 editor/assembler

I used ZEAP to port FORTH to the NASCOM. The debugger was essential.

My mind is playing tricks, for I remember having EPROMs for BASIC, and FORTH. The BASIC I bought on tape and transferred to EPROM (I think). The FORTH I ported from another assembly language and had on tape, and I think, EPROM.

The famous 'buffer' board between main and the expansion bus

This memory board never worked, despite the hacks
The serial I/O interface (cassette tape)


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