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Timex Sinclair ZX81 Back On the Market
Eugene Blanchard writes: "You still have the chance to purchase that Timex Sinclair ZX81 computer. Someone has kept a warehouse full of them. I had a few and thought that they would make a pretty good controller board with the Z80 processor. Now let's see if we can load Linux on them! "
Heres a link to a page with details for building your own ZX80/ZX81 from scratch:h tml
http://www.home-micros.freeserve.co.uk/zx80/zx80.
I remember ordering and building my Sinclair back before Timex became involved and it became the ZX81. Wow, what a memory trip it is to think about putting together that thing... I can almost smell the 60/40 now.
Unfortunately, I never got to do much programming on mine... it had a temperature problem. After a few minutes of running, the TV would lose horizontal sync. Turned out that my ROM chip ran way too hot, and as it warmed up the TV signal went out of sync. Sinclair must have saved money on components by interleaving the sync of the ROM with the video generator, instead of having separate clocks for each. My girlfriend's techhead brother figured this out for me -- never would have discovered it on my own.
We solved the problem by keeping a piece of ice on the ROM chip, in a little plastic bag. Every so often, when the ice had melted, I'd have change the bag for one with a fresh piece of ice. Talk about your cooling problems -- and I wasn't even overclocking!
--Jim
I was at the Vintage Computer Fair last weekend, and the going rate is about ten bucks. Yes, with manuals and everything. My VIC-20 isn't even worth a quarter of that price, and that's including the original boxes, manuals, an expansion card, programs on tape, and a bunch of other cool original stuff.
By the way, the original price was... $99.95! (Oh, O.K.... they started out at $199.95, but were later lowered to $99.95. I last saw a new one in a store in New York City in the late 80s for $14.95.)
This link may be of interest to the ZX-curious. --Tom
Tom Geller
I had a few and thought that they would make a pretty good controller board with the Z80 processor.
I did a project in high school (~1985) trying to use a ZX81 as a controller for a robot. It worked, kinda. Very susceptible to emi, especially the sort that small DC motors put off. It used technology that was "good" for the time, which translated to today's technology, means "slow and power hungry."
Other than the "vintage-cool" factor, as a controller, you can do a whole lot more with a modern microcontroller. More I/O, similar amount of memory, much more in terms of MIPS/W. You do lose the video display and the ability to program it in BASIC.
The ZX81 was a great hack. The ability to implement a GUI (it did output to a TV) and an interpreter with that little amount of processing horsepower, RAM and ROM is a pretty impressive feat, especially keeping it relatively cheap.
I think that we could all learn something from the ZX81- it is amazing how far you can stretch your resources when you don't have many. The real power of such knowledge is knowing when it is appropriate to use it.
- BASIC in an 8KB ROM.
- 2KB RAM on board
- Expandable to 16KB RAM with a "backpack"
- Expandable to 54KB RAM max with some mods.
- A 40 key keyboard with multiple shift modes to get all of the characters and BASIC keywords.
- Cassette interface for program loading and storing.
- A low cost thermal printer.
This was not a serious machine; it had major shortcomings. But the price was right.The keyboards were very troublesome. The thin ribbon connector often cracked from the heat and aging, disabling the membrane keyboard. With a little experimentation you could still "pick" it with wire ties. ;-)
The cassette interface was flakey too. They recommended a mono portable cassette recorder, run from batteries. The volume level had to be "just right."
The memory backpack was troublesome as well - it wiggled too much, breaking the connection to the card edge connector on the back of the machine.
Entering programs on this machine was truly unique - you didn't type the word "PRINT". You pressed "P", and depending on where you were on the line, the BASIC interpreter knew if you were going to enter a keyword ("PRINT"), or if you wanted the letter "P". Sorry, uppercase only.
It was amazing was assembly language programmers could do with this thing. I fondly remember the Flight Simulator, which fit on a 16KB machine. There were programmers toolkits on cassette, and other little applications. Data storage was a serious problem though.
Is there an archive of ZX81 software anywhere, possibly in WAV or MP3 format? I still have my cassettes, but after 16 years of disuse I doubt that they are readable.
Mike
PS: Search on google - there are several projects out there for emulators.