OK. This is the computer that started it all for me. (Well, a rather poor picture of the actual machine…)
As you can see, it isn’t in original condition. There are a few mods and, unfortunately, the processor is missing! I think I put it in someone’s ZX81 some years ago. I’m sure I have another somewhere under all this junk…
Note that I never did build the RF modulator shown on the circuit diagram. After the first batch or so of machines were produced NASCOM started to include a ready-built, screened Astec unit which is fitted to the underside of my PCB.
This computer came fitted with the Nasbug 1.T2 monitor software, which I upgraded pretty quickly! I say “fitted”, but that’s in the broadest sense as the whole thing came as a kit. The keyboard and RF modulator were pre-built but that’s all. The kit came with two books. They became known as “the easy book” and “the hard book” – the construction manual being considered “easy” at that time!
The keyboard was rather unusual by today’s standards – and not at all easy to work with as it was driven and decoded by routines in the monitor. The keys were of the Licon magnetic transformer type. These are completely contactless. Because of the way in which this type of keyboard works it is completely free of contact “bounce”. The reset key is a standard switch type.
Pulses are sent to columns of keys (the computer sends “counter reset” and “clock” signals) and the rows read back via the keyboard matrix. Pressing a key mechanically completes the core of a transformer, allowing the pulse to pass through. Any pulses picked up are then latched and the contents of the latch read back by the computer as a 6-bit code. That code is then decoded by the monitor.
If any reader remembers a book called “The Cheap Video Cookbook” by Don Lancaster, it is instructive to compare the Nascom 1 video circuit with one of the schematics in that book. If I remember correctly they were both based on a system originally described (by Don?) in Wireless World.
The Nascom-1 was designed with little capability for expansion. A single-sided card edge connector at one end brought out various signals, but they were not buffered so were incapable of driving address and data bus signals to many external devices. In addition, there was a problem with the processor clock at the edge connector, which caused timing problems. That is where the Buffer Board came in. This was an 8″ square card which interfaced the Nascom-1 edge connector to a versatile 80-way bus system – the same one which was later native to the Nascom-2.