The Sinclair QL Forum

Hmm - I just came across an interesting little module listed on sellmyretro - a plug in module to convert RGB output to composite video / S-Video output for connection to a monitor or projector.

I should imagine this will work with the QL - I wonder if he could squeeze a Pi Zero header onto the board so it could be used for HDMI ouput...

http://www.sellmyretro.com/offer/detail ... e%29-27577

Waste of time on QL that already has composite outputs though!

I agree that at the moment for a QL it is not required (if you don't mind making up a composite video lead, or can get hold of a QL SCART lead) - however, it was more the question as to whether with the aid of a header, Raspberry Pi Zero and a bit of software, it might be possible to convert the output to HDMI

RWAP wrote:I agree that at the moment for a QL it is not required (if you don't mind making up a composite video lead, or can get hold of a QL SCART lead) - however, it was more the question as to whether with the aid of a header, Raspberry Pi Zero and a bit of software, it might be possible to convert the output to HDMI

Didn't Dave cover that in one of his extensive posts?

This is very expensive for what it is. The entire board has a value including design costs of maybe £15.

There are a few ICs that can do RGB to composite/s-video but they for practical purposes just duplicate existing functionality the QL already has. We looked at this and decided it wasn't worth doing unless it introduced new functionality, namely re-timing the mode 4 signal so mode 4 fits within a standard screen. We looked at putting an S-Video output on the SSQB but decided not to because the re-timing circuit isn't done.

You can see Nasta's thoughts on retiming the 8301 here:
http://qlforum.co.uk/viewtopic.php?f=2& ... ing#p17858

Personally, I prefer the ZX-HD approach, which is similar to what has been implemented for the Spectrum Next - however, this is Spectrum specific and attaches via the expansion socket to monitor video RAM and then uses the Raspberry Pi to generate a copy of the screen which can be viewed over HDMI (it then gets around the expensive HDMI licencing).

It would surely be possible to create something similar which connects direct to the QL's (and other computers') video out and replicates the signal - in effect replacing a QL SCART lead + HDMI upscaler...

The ZX-HD works well and decodes and copies writes to video RAM, which is a tiny area run at slow speed in the ZX80/81. I have high hopes the Pi could do this, but Nasta is unequivocal - the Pi GPIO isn't fast enough. It might well be on the Pi4, as that is one area that didn't really improve between the Pi2 and Pi3. Then, running a QL emulator on that Pi4 would be orders of magnitude faster than putting it on a QL anyway.

Dave wrote:The ZX-HD works well and decodes and copies writes to video RAM, which is a tiny area run at slow speed in the ZX80/81. I have high hopes the Pi could do this, but Nasta is unequivocal - the Pi GPIO isn't fast enough. It might well be on the Pi4, as that is one area that didn't really improve between the Pi2 and Pi3. Then, running a QL emulator on that Pi4 would be orders of magnitude faster than putting it on a QL anyway.

Hmm it is a shame that latency would cause this issue - there are a lot of 1980s computers and consoles beyond the QL which would benefit from a solution

It's not latency that causes the problem, but the sheer bandwidth of writes to video RAM is huge.

On the amiga this is solved using an FPGA to snoop the bus for video writes. Something similar could be done on most computers with a little verilog/VHDL jiggery pokery!