Sinclair ZX80 / ZX81 / Z88 Forums

Thanks for the pictures. It looks good so far. As the transistor solution this is what most people do for a simple discoupling of the video signal (in fact without the two diodes). It could be a good idea to put a second smaller resistor (47R for example) between +5V and collector to protect the tr...

Hi PokeMon, Thanks for having a look at the code. >>>Well took a look at your source but it's a bit complicate. Just three suggestions from my side: 1. You can use the variables section (printer buffer) directly when you include ZX81VARS.INC (and ZX81DEF.INC) instead of simply ZX81.INC Then you can ...

In this thread discussions about the ZX81 Nixie Clock source code. It is open source, so everyone can have a look at it and make modifications where possible. Would be nice to have a DCF77 interface connected to it, as found in the German forum. It wouldn't be of any help to me as we can't receive t...

We are not talking about 65 bytes. In a 1k program you have about 750-800 bytes free for an assembly program (with small BASIC start statement like 10 REM .... and 20 RAND USR ...) with a collapsed display file which is nearly empty. In your video you only print time in the first screen line, so di...

OK, I didn't expect to spend this much time on it but there are enough arguments to do a further investigation :-). First of all, the drawn current from ULA pin 16. I measured this compared to another TS1000 that still has the pin 16 connected to the RF modulator. In fact, the RF modulator draws a H...

I wanted to use the keyboard to set the time for my clock (using 0 - 9, and some letters for setting hours, minutes etc). However, while programming this, I realized the program was never going to fit within 1k no more so I abandoned the idea and went for a simple basic solution (INPUT A$) and read...

Can not see in your scope pictures very good but I think the same reason gozzo meant here. The white level voltage from ULA breaks down due to a low impedance connected. This moves the adapted signal in a way with not much white level. The ULA normally puts out a range of up to 5V which is modulate...

btw. shouldn't this post be in another section/subforum? Yes, it should be moved to the Development section. I wonder if the simply reading in a game via IN instruction doesn't result in screen flickering as the line counter should be reset by IN ($FE) and this process is not synchronized. :shock: ...

Not using a buffer could be the reason why you had a dark picture , the video input of your TV was loading the ULA's output too much, if it was buffered with an emitter follower OR a video op-amp/buffer I've come across, the AD817AN , (not yet tried it, though), it would probably be ok. Not so, the...

Even simpler if you leave the modulators innards there, no need to remove them. However I don't really like the idea of not buffering the video, and isolating it with a capacitor, but if it seems to work ok and the ULA isn't being overloaded, then its great ! I didn't think about that as I had firs...