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ppppenguin · 3rd Mar 2006, 9:06 am

Kat

Unlike so many folks who have suggested using a PC for standards conversion you have the technical knowledge to do it if it's possible.

The main problem as I see it is getting a sensible 405 waveform. Ignoring DVI which isn't relevant here, the outputs of graphics cards are either RGB or, in some cases, PAL/NTSC. Unless the PAL/NTSC coder in the graphics chip is very programmable* I think you will have trouble getting a sensible 405 line waveform out of it. For monochrome you would use the Y part of an S-video output but it's quite likely that the line and field lengths will be "hardwired". The RGB outputs are more promising since they are usually highly programmable. A small amount of analogue circuitry would be needed to add syncs and generating composite 405 sync might be a problem.

A colleague has a lot of experience of getting graphics cards to run at funny resolutions. He once made a BBC-B work at 405 (I tried this years ago when I had one) and has made DVI outputs do almost impossible things. He reckons it was hard getting the DVI output to run at 720*576, 50Hz (CCIR 601) though this varied between different graphics cards.

I'm not saying it's impossible, just pointing at some of the likely problems and wishing you all good luck.

*Some cards may have a separate PAL/NTSC coder. David Robinson has succeeded in making the ADV7171 do 405 out (not on a graphics card) but it took a lot of ingenuity. I tried and failed even though I knew the chip pretty well.

3rd Mar 2006, 9:06 am	#2
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: PC as a standard convertor Kat Unlike so many folks who have suggested using a PC for standards conversion you have the technical knowledge to do it if it's possible. The main problem as I see it is getting a sensible 405 waveform. Ignoring DVI which isn't relevant here, the outputs of graphics cards are either RGB or, in some cases, PAL/NTSC. Unless the PAL/NTSC coder in the graphics chip is very programmable* I think you will have trouble getting a sensible 405 line waveform out of it. For monochrome you would use the Y part of an S-video output but it's quite likely that the line and field lengths will be "hardwired". The RGB outputs are more promising since they are usually highly programmable. A small amount of analogue circuitry would be needed to add syncs and generating composite 405 sync might be a problem. A colleague has a lot of experience of getting graphics cards to run at funny resolutions. He once made a BBC-B work at 405 (I tried this years ago when I had one) and has made DVI outputs do almost impossible things. He reckons it was hard getting the DVI output to run at 720576, 50Hz (CCIR 601) though this varied between different graphics cards. I'm not saying it's impossible, just pointing at some of the likely problems and wishing you all good luck. Some cards may have a separate PAL/NTSC coder. David Robinson has succeeded in making the ADV7171 do 405 out (not on a graphics card) but it took a lot of ingenuity. I tried and failed even though I knew the chip pretty well.