Outputting composite video to HD-15?

[Kenisav]

There are scores of places on the Net selling an inexpensive adapter cable that plugs into a PC's 15-pin VGA-out and splits off to RCA TV-out. This adapter, they all claim, "works with laptops and desktops with VGA cards that have TV-Out function capability through the VGA connector". I never heard of a graphics card that could do that and I still can't find one by doing a search for such a device thru Google Products. It's quite a source of confusion. Maybe they mean that adapter to be used for some rather-specialized equipment/application and not for your ordinary PC looking to have TV-out.

I'm very curious. Does any of you swamis know the answer, please?

[Tomi Engdahl]

The trend of "adapter cable that plugs into a PC's 15-pin VGA-out and splits off to RCA TV-out" started with Matrox Dualhead grphics cards very many years ago. Matrox built a series of graphics cards with two VGA connectors on the back. The first one was for normal PC monitor. The second was could be configured to work with normal PC monitor (the default configuration) or it could be set to a special mode where it outputted composite video and S-video signals through VGA connector on pins that normally carries RGB signals (so could be connected to TV with the 15-pin VGA to RCA TV-out + S-video out cable supplied with the card). The trick to generate the TV output was a special RAMDAC IC on the card that could be configured to output either RGB or those TV signals (composite video, S-video).. Normally it outputs RGB like normal VGA outputs. But when the RAMDAC is put to TV out mode and graphics card controller handling the output to second monitor timings are set to match TV output needs, the output signal is suitable to TV.

I have heard that some other graphics card manufacturers have copied this same idea to their products (for example some laptops where the built-in LCD is the first display and second output is that VGA connector on back).

Maybe they mean that adapter to be used for some rather-specialized equipment/application and not for your ordinary PC looking to have TV-out.

That's what they mean.

[Kenisav]

Yo many thanks, Tomi Engdahl