Recreating the Compukit UK101 (1)

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There are three computers responsible for my eventual career in software. The Compukit UK101 is one of the three, ranking alongside the first computer I used (a Research Machines 380Z at Friesland school) and the first I owned (a Sharp MZ-80K).

The UK101 is an interloper amongst the Z80 based machines on this blog of course – as there’s a 6502 at its heart. But no matter. The series of articles published in Practical Electronics in 1979 describing this computer got me hooked. I didn’t own one at the time, but I did manage to snag one of the 5,000 sold from a well-known auction site ten or more years ago for £60. I still have it and it works, but like any electrical equipment that’s 40 or more years old it doesn’t seem wise to use it for a prolonged period.

I retired in May this year. One of the projects I’ve been working on since is using Grant Searle’s FPGA-based design to recreate a version of the UK101 that doesn’t make me worry that I’m about to electrocute myself when I use it. I’m pleased to say that it’s been a successful build. I now have a UK101 replica running on an Altera Cyclone II FPGA board plus an expansion RAM chip, giving me a 40K beast to play with.

The finished UK101 replica, housed in an old takeaway box. It uses a PS/2 keyboard, composite video output and a serial connection to a PC to simulate tape storage.
The finished UK101 replica, housed in an old takeaway box. It uses a PS/2 keyboard, composite video output and a serial connection to a PC to simulate tape storage.

In 1979 an additional 32K memory would have cost an extra £196 + VAT over and above the £219 + VAT for the 8K included in the kit, according to the copy of the UK101 manual. The AS6c1008-55PCN memory I’ve used for the replica was a mere £6.99 including VAT and postage. The FPGA board cost less than £20, a USB blaster programmer was another £8 and I spent £10 on a mini PS/2 keyboard. The serial adaptor was £12. I probably used another £10 worth of components from my stock (stripboard, resistors and sockets). The case was free – it originally held a takeaway curry. A little under £70 all told – compared with the £2,600-ish in today’s money that the original machine would have cost. A bargain.

She lives! The unexpanded project running using 4K RAM onboard the Cyclone II FPGA

I’m going to document the process I followed to build the replica here, as well as talk a little bit about the software I’m getting to work on it. So this is the first of a few articles.

To the Z80 purists I apologise, but only a little. My blog, my rules, after all.