Sinclair ZX80 / ZX81 / Z88 Forums

Hello wizards! I tried the "why wait" mod on my issue 3 ts-1000 (using the default 2907 transistor) and it worked perfectly fine for long minutes, a sweet 10% speed boost and stable picture. But when using it with my ZXPand+, I would get progressively more RAM corruption whenever I would shift-reset...

Well done! The best Galaga-style game I've played on the Zeddy. I haven't managed to make it work with my zxpand joystick but I'm still figuring that out so maybe my fault. I don't have UDG or Chroma, just needs a catchy song on the zonx to be as good as can be (unless you make it hi res without ext...

I must persist :) I think I have a heat stroke, my brain isn't working very well so I just can't stop thinking about this. :) The zx81 expansion port has basically all the signals a clock doubler needs, /IORQ, /HALT, WR and so on, and of course /CLK. Could a simple expansion be made to hold the logi...

Okay, my idea was to assume that the required clock pulse would follow a predictable pattern, 3.25 Mhz when displaying a char, 6.5 Mhz otherwise, so you could literally write a program with a line for every pixel or scan jump to generate the clock pulse or skip it (for half speed). Run the MC at 6.5...

"Randy" = Andy Rea, doh, thanks for sorting me out, seems obvious in hindsight. :) As for hardware requirements, as far as I can tell the ZXpand+ can handle 6.5 Mhz so RAM speed shouldn't be a problem? The whole idea of the Baker/Rigter "clock doubler" is to drop down to "SLOW" 3.25 Mhz clock whenev...

Hi everyone! I'm hardware-innocent and for the two days I've been looking into clock doubler designs that I could build cheaply and easily. Unfortunately even the simplest and latest designs from Wilf date from 2003 and still needs 3 IC and enough ability to be able to build the circuit correctly. T...

Bienvenue Olivier!

Je vais sur old-computers.com presque tous les jours, très bon site!

Another visitor? Stay a while... Staaaay forever!

The digitized death yells on Impossible Mission were so impressive on the C=64 that one day my big sister rushed down the stairs fully expecting her little brother to be crispy & smoking.

Great design on the port even without sound.

Because nothing compares to a real Cherry Keyboard with ZX81 professional printed keycaps. :mrgreen: My homemade keyboard has Cherry keys (well... Chinese Cherry, I ripped out the keys from the cheapest keyboard I could find :) ) but I haven't figured out how to "professionally" print the keycaps. ...

That looks like the keyboard from a TI 99/4A with extra timer circuitry for repeats & new functions. See TI99 keyboard adaptation for wiring help without the new circuits.

TI99/4A's are more common than Zeddies so why not sacrifice one to do this. O