Sinclair ZX80 / ZX81 Forums

Keep in mind that Sinclair contracted out the supply of power supply units to more than four companies. The label that was fitted, varied depending on which company made the PSU and which market (country) it was intended to sell it in. The ZX81 “700” and the “1200” appear to use the same size transf...

Also try... [ZX Spectrum version] 10 FOR A=0 TO 1 STEP 0 20 CLS 30 INPUT “Line number? ”;L 40 INPUT “Column number? ”;C 50 PRINT AT L,C;”O” 60 PAUSE 4E4 70 NEXT A [ZX81 version] 10 FOR A=0 TO 1 STEP 0 20 CLS 30 PRINT AT 21,0;“LINE NUMBER” 40 INPUT L 50 PRINT AT 21,0;“COLUMN NUMBER” 60 INPUT C 70 CLS...

Try... [Works on both the ZX Spectrum and the ZX81, but the Zeddy takes a bit longer...]

Mark

In regards to the 4116 16k byte DRAM boards, I get the impression that the one that does not use a solder mask is the earlier of the two, as it does not use plated through holes. Whereas the board with the solder mask, does use plated through holes. Maybe a company started making the first version, ...

WoW! Various circuit designs were used in the past to obtain a -5V supply from a positive supply rail. The power required by 4116 (and equivalent) DRAM chips on the -5V is not very much (it is a bias supply). 4116 (and equivalent) DRAM chips actually run most of their internal circuitry from the +12...

PRINT AT line, column

E.g.
PRINT AT 11,15;”Hi”
will print Hi in the middle of the screen.

PRINT AT 0,0;
will set the current print position to the top left corner.

PRINT AT is shown in the manual here.

Mark

In terms of graphics, imagine you are looking at a piece of graph paper (with a fine grid printed on it). X is then the horizontal plane, with point zero on the bottom left, and as you move to the right, X increments upwards. Y is the vertical plane. Point zero is still the bottom left. As you move ...

Wilf goes into considerable detail about the ZX81 video system here ;-) Yes, we know that the pages are full of ? symbols (discussed on here a while ago). In order for RAM to be hi-res capable, it must output data during both the Z80 read cycle and during the Z80 refresh cycle. So when either /RD is...

Mark

I’m not sure if there is another source for ready made ZX81 edge-connectors, but I posted some sources for ZX Spectrum ready made edge-connectors over on Spectrum Computing forums.

Mark