How to configure Xfree86 for use with TV

One interresting application for VGA to TV converter is to use it with Xfree86 X-windowing system running on Linux operating system. This free X-windowing system provides plenty of configuration options in it's Xconfig configuration file. You can easily modify the parameters of the display just by editing that configuring file with any ASCII file editor. The Hitchhiker's Guide to X386/XFree86 Video Timing is a good document to read to really understand the video configuration process.

Sample configuration for Cirrus SVGA cards

Tomi Sarvela has made a suitable configuration for running 704x552 Interlaced screen mode in PAL televisions using Cirrus 5434 SVGA-card. This configuration does not work on Cirrus 542x based SVGA-cards, because they don't have good enough clock programming capabilities. But all chips in Cirrus 543x series should theoretically work.

To add this TV mode, you simply add the following file to your Xconfig file and start the Xfree86 then in mode "PALi":

ModeLine "PALi"       13.5  704 720 792 864  552 572 605 625 Interlace

That same configuration has been also tested to work well when VGA card is directly wired to Commodore 1084 color video monitor RGB connector. Because that RGB connector has separate HSYNC and VSYNC pins, only suitable wire was needed (no active electronics).

VGA                        Monitor
Pin   Description          Pin
1     Red Video            4
2     Green Video          1
3     Blue Video           5
5     Ground               3
13    Horizontal Sync      2
14    Vertical Sync        6

I have received comment that the Tomi Sarvela's modelines do not work correctly on some PAL TVs. Santiago Garcia Mantinan ([email protected]) recommends using the following modelines for PAL TV:

Modeline  "MaxTV"       15.00   688 768 800 960  516 529 537 573 Interlace
Modeline  "640x480xTV"  15.00   640 728 792 960  480 509 517 573 Interlace

You must notice that the modes above are not 50Hz modes but 54Hz. Santiago's TV did support it nicely and you can try if your TV will do it also. To make those modelines to 50 Hz just put 625 lines instead of the 573 and then center it and you have a 50Hz mode!

Matrox Xfree86 settings

Re-use of your old CGA monitors with X-Windows/Console/Win95 article by Philippe Lantin has Matrox Millenium settings Xfree86 (X-windows), text screen (using SVGAtextmode) and Windows 95 for VGA to TV operation in NTSC TV.

Using DOS drivers for getting Linux textmode to TV

Paulo Sergio Coelho's VGATV driver can be use under DOS and also under Linux. DOS VGA to TV driver can be used to be able to get the Linux cosole to the apropiate frecuencies for your TV. The process is simple:

Start computer in MS-DOS mode
Load the VGA to TV driver
load Linux through loadlin

Now the Linux console on text mode will look just like the DOS text mode screen looked, even if you start X or launch dosemu when you come back from this linux restores the VGA registers, so everything looks great.

The problem with dosemu is that it starts with a vga startup, so the boot process is carried out like a DOS one and you need to load again the driver under dosemu to be able to see the dosemu stuff ok, but even though you don't load it if you come back to linux the screen will be OK.

Tomi Engdahl <[email protected]>