Sinclair ZX80 / ZX81 / Z88 Forums

Just a quick question: If you take an unmodified ZX81 (read: video output via VHF/UHF modulator), a good old CRT, and the ZX81 enters Fast mode, what is seen on the screen? I keep 'remembering' :? that in this case the CRT would output 'snow' (random pixels), same as between TV stations when searchi...

For the edge connector, try using clean paper (no ink, fingerprints or 'glossy' layer etc). This acts as a very fine / very mild sandpaper. With no solvent of any kind. 8-) Regular printer paper works well. At first you'll see the paper catch black dirt, simply continue with another piece of clean p...

Just get a CMOS version (Z84 C 00xx), it'll run cooler. I've even had East-German Z80 clones (UB880 = 2.5 MHz version) working in a ZX81. Which isn't surprising since a 2.5 -> 3.25 MHz overclock is quite moderate by Z80 standards. 8-) Working fine in ZX81 but problems with peripherals attached = pro...

Just checked the above pdf. For some reason cbmbsw included the pinout of a 2K*8 PSEUDO -static RAM (a dynamic RAM with static RAM like pinout), which is USELESS . The only ZX81's that came from factory with 2K installed were TS1000's, and the RAM chips used there are standard pinout 2K*8 static (no...

Just go with the ZX81 schematic, and datasheet for the exact RAM IC's that are fitted. These are either 2 pieces 1K*4 bit RAMs, or a single 1K*8 bit RAM (or 2K*8 in the case of a US-sold TS1000, with LK1 wire link in LK2 position). All those RAM chips are static RAMs and have standard pinout. So unl...

Filename is useful when there are multiple programs on a tape. Or a program consisting of several parts (somehow). But... nothing that couldn't be handled using a tape counter. If not using an MP3 player...

Outside that, LOAD "" works just as well.

"Factory sealed"? Don't think I've ever seen original Sinclair boxing that included plastic wrapping as shown. Although I might be mistaken. I haven't seen that many original Sinclair unboxings... (let alone ZX80) :lol: But yeah more probably a previous owner wrapped it all up, and (at best) that p...

PLCC in general is well on the way of being phased out. When it's got more than a few pins, it's mostly QFP or BGA housings these days. Personally I like keeping a few PLCC parts around for development purposes. But that's about it. Wouldn't consider 'em for any type of series production. Not to men...

@sirmorris: Cypress MAX ePLD != Altera MAX. Different CPLD family, different manufacturers. Cypress doesn't seem to do CPLD's or FPGA's anymore these days... The way I see it: So much obsolete that original manufacturer doesn't even mention it anymore on their website. Software, datasheets, family o...

ULA pin 22. Has an internal pull-up. Optionally pulled low by (external) resistor R30. Pin readable as bit 6 of I/O port FEh. The ZX81 ROM uses this bit to set system variable MARGIN (address 16424), which holds the number of blank lines in the top & bottom border. With the ULA pin low (R30 present)...