[Openchrome-users] PAL modes and vx800

[Paul Gardiner]

Anders Gunnarsson wrote:
> On Thursday 05 February 2009 11:37:42 Tim Williams wrote:
>> 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.
>>
>> to fit inside a standard plastic scart plug. However my experiments
>> 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
> 
> Hi Tim,
> 
> Thanks for your answer!
> 
> I have a cable just like that one so that would be my first option to use. I 
> could use a converter, but in that case I would like it to be a little bit 
> better. I would like it to follow the refresh rate of the input, 50 or 60Hz 
> and to have scart output or component.
> 
> One id?a would be to double the dot clock and the horizontal resolution with a 
> 1440x576 at 50i mode. I have found some positive feedback on that so i tried to 
> get i working. But get a "vertical timing out of range" for that mode.
> 
> Where can I find supported timings, dot clocks, etc for the vx800?

I've used the 1440x576 trick, not because the card I was using didn't
support the low dot clock, but because it seemed to give a slightly
better picture (although that could be my imagination - I can't explain
it). All you have to do is take a correctly timed 720x576 mode and
double the clock plus all the horizontal values, leaving vertical
unchanged.

Here's some modes I have had work:
ModeLine "1440x576" 27.0 1440 1464 1590 1728  576 581 586 625 interlace
-hsync -vsync
ModeLine "1440x576" 28.0 1440 1518 1648 1792  576 581 586 625 interlace
-hsync -vsync

I haven't had much luck with nVidia cards, but some ATI cards/chips work
fine using the radeon driver (not radeonhd).  A really good choice is
a mobo with an integrated X1250. Works beautifully.

Cheers,
	Paul.