Modelines

[tomhollis]

I apologise if I am posting to the wrong place, but I hope someone may be able to help me.

I am running Red Hat 9.0 with a Geforce 2 MX and am attempting to output through a projector.

I have a cable which goes from VGA to 5 BNC connectors and can link the projector up, however the output is not correct, even in VGA.

As it turns out, the Projector can only cope with up to 16KHz horizontal Frequency which is lower than VGA
The maximum resolution for the projector is 480i, whatever that means

Can anyone suggest a modeline I might use to get this working or point me in the right direction?

Thanks

Tom

[leibold]

Originally posted by tomhollis
As it turns out, the Projector can only cope with up to 16KHz horizontal Frequency which is lower than VGA
The maximum resolution for the projector is 480i, whatever that means

It sounds like you have the specifications for the projector (which can be the hardest part to get). The 480i means that the projector only supports 480 lines of resolution in interlaced mode. This is not unusual for a projector primarily designed for TV signals. There are websites with modeline generators you could google for. If that fails try posting the remaining specifications for the projector.

[tomhollis]

What other information would be needed?

I have posted what I know, and all the modeline generators I can find need stuff like pixel rate which I don't know

Can these things be calculated from something else?

Tom

[leibold]

Try this one:
Mode "640x480i" 10.09 640 648 664 688 480 481 482 489 Interlace

This will only be a 60Hz refresh (30Hz Interlace), but that might be exactly what your projector needs if it is indeed intended for NTSC TV applications. The horizontal rate is 14.67kHz which is within the limit you specified.

Have you checked the HOWTO ?

The reason many modeline generators ask for the pixel rate is that older videocards often only had a few fixed pixel clocks that you could use. This made for an additional challenge in matching videocard and monitor specs. Any modern card will have a programable clock generator so this is not an issue (unless you try to exceed it's maximum).

[kow]

You can try interlace modelines, but the interlace feature in the 4xxx drivers and maybe earlier is broken. Hopefully this will be addressed in the next release.

For more info to help you with online modeline generators, I believe you can search for a document floating around on the web called "Xfree video timings howto" (?). If that's not the title it's something close. That will define some terminology for you.

Pixel rate, I believe, is just how many pixels your card can pop out on the screen per second. You can specify a value for this in a modeline as long as it is within a valid range (Xfree86 log has info on this). My experience is that most nvidia cards' range is something close to 12MHz up to 350MHz. That's 12 million - 350 million pixels output per second.

I think people use pixel rate, pixel clock, and dot clock interchangeably.

If you see leibold's last post his pixel clock is 10.09. I don't think that will be within the valid range. I would expect for startx to fail, and that you'd be able to see errors in your XFree86 log file complaining that the pixel clock is wrong.

Hope that helps some, and I hope the interlace feature in the Nvidia linux drivers gets fixed. The feature might not be as important as it used to be, but it is still useful to many people.