At the end of the 1970s, the 8-bit home computer market had been under way for several years. Companies like Apple and Commodore had produced machines that retain a cult following to this day, and there was plenty for the computer enthusiast to get to grips with. As always though with a new technology, the trouble was that an Apple II or a Commodore Pet wasn’t cheap. If you didn’t have much cash, or you were a young person with uncomprehending or impoverished parents, they were out of reach. You could build a computer from a kit if you were brave or technically competent enough, but otherwise you were out of luck.
As you might imagine, the manufacturers understood that there was an untapped market for cheaper hardware, so as we entered the new decade a range of budget machines that appeared to satisfy that demand. Gone were internal expansion slots, dedicated monitors and mass storage, for cheap keyboards, domestic TV monitors, and home cassette recorders. 1980s teenagers would have computers of their own, their parents safe in the knowledge they were educational while the kids themselves were more interested in the games.
The veteran British budget electronics entrepreneur [Clive Sinclair]’s first mass-market home computer offering was the ZX80, a PCB stuffed with 74 logic chips and a Z80 processor, with a membrane keyboard occupying one end. Its flimsy white plastic console case and characteristic blanking of the display while it did any work failed to endear it to consumers, but it set the basic architecture for [Sinclair]’s ZX line of computers including the wildly succesful ZX Spectrum.
If you want the ZX80 experience the real thing is rather rare, but thanks to Tynemouth Software there is a chance you may soon be able to get your hands on a modern version. They’ve produced a prototype of a ZX80 in the form factor of a ZX81 main board, and their write-up makes for a very interesting read.
The UHF modulator of the original is gone, replaced by a phono socket for the video output. Also missing is the ZX expansion edge connector, and the 3.5mm jack used by Sinclair for power has been replaced by a more conventional power connector. This is a first spin of the board, and they admit to a couple of errors. A line between chips is missing, and a keyboard connector is reversed.
The original machine’s 1K has been upgraded to a healthy 16K so there is no need for a wobbling RAM pack, and both ZX80 and ZX81 ROMs are on board. The ZX81 circuitry for SLOW mode is missing though, so gaming will be off the cards on this machine.
Perhaps most interestingly the original 74LS chips give a far better performance than the newer 74HC variants. It seems the original’s economy of components was dependent on the analogue properties of the LS series. In an age when every possible custom chip is at our disposal we sometimes forget how far the designers of those days had to push things to reduce their BoM costs.
There is a promise of more to come in future versions of this board, so it’s one to keep an eye on. Meanwhile give it a read, for it contains a fascinating fun-down of the design of a venerable budget computer.
This appears to be the first ZX80 we’ve featured here, but we’ve brought you ZX81 projects aplenty. There was this ’81 networked with an ESP8266, or this vintage Maplin I/O board completed 30 years later.
Via Hacker News.