How to configure Linux Xfree86 for use with TV or Amiga monitor

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. Read

The Hitchhiker's Guide to XFree86 Video Timings for more complete description of the 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

If you make Xfree86 TV settings for some other graphics cards or graphics modes tell me how you succeeded in it. I can put more settings to this page if you e-mail them to me with short description and give rights to put them on this page.

How the configuration is tested

The configuration above is tested with standard PAL TV. The 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 was needed).

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

Amiga monitors are driven just like TVs so normal VGA to TV drivers work nicely with them. Here are typical specifications of Amiga monitors:

Line frequency: 15625 Hz
Raster frequency: 50 Hz (47 - 62.5 Hz)
Resolution: 640 x 200 pixels (on RGB input)

The vertical resolution can be doubled if interlacing is used.

Other Amiga monitor pinouts

Some other Amiga monitors can have somehow different pinouts. SOme Amiga monitors have SCARt connectors in back of them so my original VGA to TV circuit suitable fot those directly. One popular Amiga monitor is Philips CM8833-II which has following pinout:

 -Pin-    -TTL-         -Analogue-
   1      Ground        Ground
   2      Ground        Ground
   3      Red           Red
   4      Green         Green
   5      Blue          Blue
   6      Intensity     Fast Blanking
   7      Not used      Composite Sync
   8      H. Sync       H. Sync
   9      V. Sync       V. Sync

The analogue TGB input is directly suitable to be used with VGA card because it has R, G, B, HSYNC and VSYNC inputs. VGA card can be directly wired to this connector and visible picture can be achieved when VGA to TV drivers are used. According the monitor pinout specifications it seems that the following wiring might work (I have not tested this):

VGA pin     function    Monitor pin
  1         RED            3
  2         GREEN          4
  3         BLUE           5
 13         HSYNC          8
 14         VSYNC          9
6,7,8,10    Ground        1,2

The ground pins are connected together. It is a good idea to have many wires to carry the ground in the cable (use one wire for each ground from VGA card) and connect them together in the amiga monitor and connect them to pins 1 and 2.

Tomi Engdahl <[email protected]>