Sinclair ZX80 / ZX81 / Z88 Forums

bola_dor wrote: ↑Sun Mar 22, 2020 12:30 am Have in mind that this being an argentinian version is 50Hz (PAL-N).

Are you sure about this? The Astec RF modulator on this board sure looks like a USA version supporting channels 2/3, which means it's a 60Hz NTSC output, not 50Hz PAL.

Z80 PIN 26 HAS 4.35v But when I attach the logic probe it falls to 2.2v . So the probe is messing things up.. I'll exchange the IC with a proper TTL one .. and perhaps a diode to the probe? One with no significant tension drop? (I don't known witch).. And retest... Z80 is working good in another bo...

OK I've made myself a Logic Probe with this schematics but used a 74HC04 and a 2N2222 as that whas what I had at hand received_2644523002495580.png What I've tested ULA pins: 14 when I reset Pulses for 2 or 3 seconds and then remains Low 16 P clearly 35 High . . . IF Z80 is pulsing does it means re...

Cool stroebeljc ! Thanks for this code. It able to update the Parrot SPO sound card on the VB81 emulator. I had to add the &4F IORQ to the VTR/Mageco (@&3F) sound card, enclosed in the emulator. :ugeek: Vb81 is now update for the Parrot SPO256...(r. 08/05/2020) SPO on the &4F IOrq (IN & OUT) port. ...

But 0x4F does set bits A4, A5, and A7 to zero, while keeping all the other bits at 1 to reduce the likelihood of hardware conflict. Why anyone would use 0x03 I don’t know, that’s just asking for trouble. Mark You are totally correct. The problem is that the original guidance from the makers of the ...

It able to update the Parrot SPO sound card on the VB81 emulator. I had to add the &4F IORQ to the VTR/Mageco (@&3F) sound card, enclosed in the emulator. :ugeek: SPO on the &4F IOrq (IN & OUT) port. Select the sound card, and reinit the computer. Note that the typical port used by the Parrot is &0...

For those interested, here is a ZX81 program I wrote 35+ years ago which has support for the Parrot speech synthesizer.
(It has 400 words in single player mode.)

Another thing to try, is to add an extra 1kΩ resistor. This extra 1kΩ resistor is wired from the junction of C6 / X1 (the resonator) and 0V/GND. I don’t know why it is fitted to some boards and not others. Mark I have this on my board. They must have had problems getting those resonators going with...

zx81ultra wrote: ↑Sun May 03, 2020 9:59 pm

mrtinb wrote: ↑Sun May 03, 2020 7:40 pm Q, A, O, P are used by many games.

New version with QAOP keys has been uploaded.

Can you include the updated source file?

With the ULA taken out, have you verified that the impedance at pin 35 of the ULA is 18kOhm? Well .. not.. I know ULA is OK as I checked it with other known ULA and this ULA in the other board works fine.. I changed those capacitors but remains the same.. What would indicate ULA's pin 35 impedance?...