Custom PC, Issue 174

Custom PC Issue 174This month’s Hobby Tech column takes a look at a very special eight-byte – not a typo – microcomputer, walks through turning a spare Raspberry Pi into a Nav Coin-mining cryptocurrency machine, and looks forward to the launch of the ZX Spectrum Next with a look at a deep-dive book detailing the original Spectrum’s neat Ferranti Uncommitted Logic Array (ULA) chip.

First, the Mini C88. Designed by the multi-talented Daniel Bailey as a more affordable version of his C88, swapping the field-programmable gate array (FPGA) on which he implemented his own processor core design for an Arduino Zero and the extremely clever Dynamic Binary Translation (DBT) technique, the C88 is designed to be about as simple as a computer can get. Based on a custom instruction set, the C88 has just eight memory locations of eight bits apiece and is programmed by toggling each bit using a series of pleasingly tactile switches while monitoring the process on the 8×8 LED matrix that serves as its display.

For regular readers, this will all sound familiar: the original FPGA-based C88 and its 32-byte bigger brother the C3232 were the subject of an interview back in Issue 155. While Daniel has still not turned the C88 into a kit you can head out and buy, the Mini C88 is definite progress in that direction – and, as always, anyone interested in the project should hassle him about it on Twitter.

For those with a Raspberry Pi and a desire to play with cryptocurrency, meanwhile, this month’s tutorial will be of definite interest: a guide to turning a Pi into a ‘Stake Box’ for the Nav Coin cryptocurrency. Designed as an alternative to Bitcoin, Nav Coin offers those who run network nodes rewards in the form of a five percent return on their coin holdings when locked up in this manner. Taking less than an hour to set up and requiring nothing more than a low-powered computer, it’s a great way to get involved – and the Nav Coin project itself definitely one to follow.

Finally, while waiting impatiently for my ZX Spectrum Next microcomputer to land – which, I’m pleased to say, has since happened – I enjoyed a re-read of Chris Smith’s excellent The ZX Spectrum ULA: How to Design a Microcomputer. Based on interviews and deep-dive analysis, the book investigates the tricks and techniques which allowed Sinclair Computers to build the ZX Spectrum micro at such a bare-bones cost – which, in turn, was thanks to clever use of an Uncommitted Logic Array (ULA) chip from Scottish electronics giant Ferranti. Effectively a write-once version of the modern FPGA, Ferranti’s ULA saw the number of components in the ZX81 drop to a quarter compared to the ZX80 and is key to how the ZX Spectrum does what it does.

For all this, and a bunch of other interesting things by people who aren’t me, pick up a copy of Custom PC Issue 174 from your nearest supermarket, newsagent, or digitally via Zinio and similar services.

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