Sinclair ZX80 / ZX81 / Z88 Forums

Hi there, as a question to all hardware developpers for ZX81 or people who wnat to get to. I never found an extender board which can be used for own hardware and asked some people in the german forum - told me that's not existing or never heard from. So I developed this kind of board which gives the...

Paul wrote:Sounds good to have a collective order to Germany. Please ask in our Forum. It will be helpful if YOU do it rather than I do it. They already think i would hide my Whisky orders in all the collective ZX orders i did this year

Cheers !

If it's more GBP 15.00 than GBP 1500 you can count 2 for me. :lol: I think we could do a combined order from germany for save postage. I even play in my mind to give you ULA a kick with speed in general. You don't have to change anything for me, I will just play with it and see what happens. Maybe i...

Yes I need one or two ULA too.
Do you have already an idea of the price ?
I hope it's not more than a used ZX81.

One more correction, I forget a connection between sync and backporch because they are overlapping and backporch has to be avoided during sync. I added one more schottky diode for this. Video-HQPixBasic.gif If I order electronics next time or stay in the near of an electronic shop, I will test it. N...

Fine Thommy, sounds good what you want to do. 8-) So all in the ZX81 or ZX80 is controlled via the clock. Z80 CPU is clocked with 3,25 MHz. These means a full cycle. The CPU always do something on either rising or falling edge of the clock. So if you have about 6,5 Million messages in a second this ...

I think it will help in the beginning just to study datasheets from the used components (Z80 CPU, 2114 RAM, 38818P ROM), espescially timing diagrams and leaving out the electrical specifications. Of course it could be fun to really calculate current, voltage, resistors, capacitors or at least delay ...

As ZX81 user/lover, don't even know what an MSX is? :shock: please GO HERE! NOW! I did not find any connection to ZX81 or to Sinclair. It's just another computer like Atari, Commodore C64 (I even worked with the older PET :mrgreen: ) and more in this time. So my interest is ZX81 and I think MSX is ...

so therefore the video MUST overlap some of the Hsync & backporch, as there are only 207 cycles per scan line. Regards Andy There was a mistake in the last posted schematic from me yesterday (without LM1881). By the way I changed now following in my video schematics: 1. it's no more important wethe...

Schematic says otherwise - these 2 signals have series resistors between ULA and those ROM/RAM pins (not sure exactly why they would be needed btw), but AFAICT no pull-ups. This is used for switch off the internal RAM when putting external RAM expansion on the slot. I think You could switch off ROM...