Sinclair ZX80 / ZX81 / Z88 Forums

That's all very well, but what if you want to be able to enter '£' - which is shift +space..???!!

Hmm...maybe ...but I wanted to make an external unit - at least at the moment - but may change my mind if the size of the unit can be minimized, so 'forcing' a line would be a no-no for the moment. I do intend to try one of the circuits out as and when I get time, also have a circuit idea for a simi...

OOPS , realised I made a boob in the 'poke enabled' circuit - the link from the NAND gate output to the junction of the base of the transistor and the 22k is incorrect, the NAND output should go to the other side of the 22k resistor linked to the enable of the 74HCT541 - connect it wrong any you'll ...

Here is the 'poke' enabled circuit...

Also have a circuit idea for a 'POKE' switchable version (poke 16417(supposedly unused system variable),128 or higher to disable break, 127 or lower to enable) will post pic soon! I may actually try this one!

Another possible circuit - using an EPROM as an address decoder(not sure if that would work, but don't see why not) - only 2 chips needed plus a few other parts!

According to the disassembly listing of the zx81 rom, the break detect code is from 0F46 to 0f4A, being LD A,7F IN A,(FE) RRA when break(space) is pressed, carry is reset, but if not pressed is set. So I was thinking if the RRA is changed to SCF (set carry) carry will always be set and break would n...

The only way I can think of doing it at the moment is to 'patch' the break(space) detect code in the ROM - I think it was a silly idea to use the space key as break, I'd have preferred to use the EDIT or FUNCTION also as break. I'll have a look into it to see if it's possible to make a reasonably ea...

I can't even remember if it worked or not - I bought 4 zx81's with various other bits(mostly 16k rampack pcb's - with hacked off edge connectors!) in a box cheap many years ago - I did test them and stuck a label on each one to say what fault it had, I think there was at least 1 duff ULA, 1 duff Z80...

That's the beast!! Well, 90% sure!! Will dig it out and have a look when I get time!!