Sinclair ZX80 / ZX81 / Z88 Forums

The connections to the cartridge slot will be the same as the Sinclair Interface 2 (see here ). I expect the push button switch to simply be a reset switch wired between the /RESET line and 0V/GND. The joystick port will be wired to the Atari pin-out, and the Kempston I/O protocol (input on port 31)...

Technical question, is there any way that this could be included to run with the ZX81 emulator on the ZX Spectrum Next? It looked like I could just switch one ROM image for another but on the ZX Next SD Card the ROM image is 32K. I could maybe see why the Next may have a 16K byte ROM image (that’s ...

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Mark

The ZX1541 that I ordered arrived on the 5th of February, but I have not yet had any time to play with it

Mark

It has just occurred to me that I have never got around to posting up photos of the one I built using the PCB that was kindly supplied by SirMorris

I’ll try to correct that omission this weekend. But no promises.

Mark

Would I be right in thinking that if I were to lift R59 and the -ve lead of C44, this will completely isolate the DC-DC converter from the rest of the board supplied by 12V? Would this be a sensible next step to seeing where the short is? No. If R59 is okay (1.8kΩ, although an in circuit test will ...

Yes, I believe at least three exist. Lardo has one, I have one, and TMAOne has one.

Mark

The address decoding done by the ULA (for the ZX81, TS1000) and logic chips (ZX80) only uses CPU address line A14. A14 LOW selects ROM A14 HIGH selects RAM. Sinclair used a 8K byte ROM chip, the decoding puts it at 0x0000 to 0x1FFF. But also at 0x2000 to 0x3FFF, 0x8000 to 0x9FFF and 0xA000 to 0xBFFF...

Lifting one leg of R62 will split the +12VA (analogue) supply from the main +12V supply.

C1 to C4 are for the -5V supply, C5 to C8 are on the +12V supply.

Mark

The ULA only provides very basic ‘partial’ decoding of the memory. To increase the RAM above 16Kmeans additional logic (chips) are required. In theory there is no reason why the internal RAM cannot be expanded to 56K bytes. However, not many people have done this. Hence it may be difficult to find a...