Newsgroups: sci.engr.television.advanced
Subject: Re: SCART connectors...
References: 
[email protected] (Chris Smowton) writes:

> I know this is a little off topic, but this seems like as good a group
> to ask in as any...
> 
> A few qustions about SCART's video modes...
> 
> 1) Does SCART carry a composite video signal? Is this "CVBS"?

Yes. SCART can carry and carries normally composite video.
CVBS is just one name for composite video.
 
> 2) Why do all TVs have 1 scart socket supporting RGB and one
> supporting S-video? Why not have all the pins connected on both, then
> give the user a choice of which video signal to express?

The RGB and S-video both signal formats use partially same pins. 
This means that if same input needs to support both S-video and
RGB, the input electronics needs to have some smart electronic
switching of the signals of same pins to different places in
TV chassis depending on if composite video, S-video and RGB are
used.

The operation of swithing between composite video and RGB is well
standardized and easy to implement. There is a pin "fast blanking"
which is essentially a switch signal which controls TV to
either to use signal from RGB input or from it's internal
composite video decoder. The sync signals are always taken
from the composite vidoe pin, no matter if mode is composite video
or RGB.

Adding S-video to this picture made thigns a mess..
There is no nice identification method for the TV to identify
automatically if the incoming signal is S-video or composite video
(some rare TVs try to do this automatically with more or less success).
Practically user needs to always know if devices support S-video,
where to connect to, what settings to use etc. to get proper
picture. If you just plug in, you will very easily ghet just
black&white picture with S-video on SCART unless everything
is set and wired correctly.

(for comparision with composite video / RGB
switching everythign works automatically without worrying,
always at least composite video quality with colors and better RGB 
picture automatically or after some setting).

> 3) Do TVs with just one SCART support RGB or S-video through the SCART
> socket?

Varies from TV to TV. Some support and some don't.

> 4) Can most TVs select to display composite or S-V/RGB?

Most TVs can support composite video and RGB.
Most new TV can also support S-video in addition to composite video and RGB.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/