[Openchrome-users] PAL modes and vx800

[Tim Williams]

On Wed, 4 Feb 2009, Anders Gunnarsson wrote:

> As I understand you need support for a slow rate on the dot clock, around
> 14MHz. Both open chrome and the via drivers give me "Clock range:  20.00 to
> 230.00 MHz". Does that mean I'm smoked?

As an experiment I built a convertor circuit (using the 
design on http://www.nexusuk.org/projects/vga2scart) a year or two 
ago. Cost very little and it works beautifully, I built it small enough 
to fit inside a standard plastic scart plug. However my experiments 
proved that you need a dot clock of ~14Mhz to get it to work. Haven't 
tried it with an OpenChrome driver, it worked with the Nvidia card on my 
regular desktop, but failed with the intel chip on my laptop and the 
permedia 2 on my server, neither could manage the necessary dot clock 
rate.

I suspect the 20-230MHz range of the driver is caused by a hardware 
limitation, rather than an issue with the software. Your best bet is 
probably something like 
http://www.maplin.co.uk/Module.aspx?ModuleNo=35258, which essentially does 
the same thing that the tv out hardware on many graphics adapters does, ie 
it converts the signal down to something the TV can cope with so that the 
graphics card doesn't need too.

Tim W

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