CPLD replacement for ZX8301

[Cristian]

Would it be too difficult to have 8 colors in mode 4?

This would be the Holy Grail
Anyway, even just the possibility of using different colors in Mode4 (and get rid of the green/red stipples) is a really great goal in my opinion.

[lliont]

Would it be too difficult to have 8 colors in mode 4?

It needs more memory to do this, maybe using the second screen memory and Minerva second screen option but there is a more serious limitation and that is the memory access speed.
It needs an fpga but I won't go there (yet).

[Derek_Stewart]

When does Derek start assembly of them

Thank you for the vote of confidence, I could help if required.

[thorsinclair]

Would it be too difficult to have 8 colors in mode 4?

It needs more memory to do this, maybe using the second screen memory and Minerva second screen option but there is a more serious limitation and that is the memory access speed.
It needs an fpga but I won't go there (yet).

Am I right to assume that if you were to add more memory and a FPGA there would even more colors be possible ein Mode 4 and 8 and that this would rather be a 'graphics card' instead of a replacement board?

[lliont]

It would be both, but I don't think it's worth doing. It would be much more expensive to build and again not supported by the existing software.
Well it could be done with a much larger cpld or better with an fpga that has internal ram but anyway with a more expensive IC.
I think a small cpld as a replacement of a faulty ula adding a few extra features is enough for a standard QL.

[lliont]

You know what would be nice to add ?
Sprites!

[M68008]

Am I right to assume that if you were to add more memory and a FPGA there would even more colors be possible ein Mode 4 and 8 and that this would rather be a 'graphics card' instead of a replacement board?

Yes, and as an aside (I don't mean to hijack this thread) I started writing something like that (QL graphics card) for fun some time ago. I have some FPGA code running on Mister and using the QL screen format, palettes, 15 sprites, hardware scrolling and more. Very far from finished, especially as I wanted to add even more features and still doing some historical research when I have time.

[thorsinclair]

Am I right to assume that if you were to add more memory and a FPGA there would even more colors be possible ein Mode 4 and 8 and that this would rather be a 'graphics card' instead of a replacement board?

Yes, and as an aside (I don't mean to hijack this thread) I started writing something like that (QL graphics card) for fun some time ago. I have some FPGA code running on Mister and using the QL screen format, palettes, 15 sprites, hardware scrolling and more. Very far from finished, especially as I wanted to add even more features and still doing some historical research when I have time.

Cool stuff. Sounds very tempting. Would this meant to be plugged into the expansion port (normally occupied by Gold Cards etc.) or be an internal version?

[thorsinclair]

You know what would be nice to add ?
Sprites!

This would be another milestone! Great idea.

[robin7g]

Just wanted to add my 2 cents.

I was struggling to find a replacement ZX8301 chip for my broken Sinclair QL, an eBay seller wanted €40 for an original one but would not ship to me in Canada so there was nothing I could do except build one using Leon's Hackday.io project. Leon even helped me source the parts! This is the prior simpler ZX8301 replacement but it worked great. Thanks for sharing this project.

I used JLCPCB to make the PCBs. I found the Altera FPGA chip on eBay with Leon's help. You need an HCMOS/TTL level 30Mhz crystal oscillator which was harder to find than it should be but Newark's UK warehouse had them.

Fun project. I have perfect video output now and a mostly working-ish QL.

I am also looking for a replacement ZX8302 chip or schematic if anyone has any ideas.