Intel 845 and TV-out: how to switch to PAL mode?
arg-bsd at arg.me.uk
Thu Feb 19 17:47:51 PST 2004
On Thu, 19 Feb 2004, Torfinn Ingolfsen wrote:
> Yes, i am aware of that. My (old) TV only has composite and SCART input
> (and RF / antenna of course). I have tried the following combinations:
> 1) s-video out from pc, via an s-video to composite adapter, to
> composite input on TV.
> 2) s-video out from pc, via a s-video to SCART adapter, to SCART input
> on TV.
> 3) composite out from pc, to composite input on TV.
> All combinations result in a b/w picture, both in console and in X.
I know nothing about the Intel 845, but can offer a few hints about
S-video and SCART connectors:
- S-video provides two video signals: 'Y' and 'C'. The Y signal is
the luminance and syncs, so is equivalent to a composite video
signal for a b/w picture. The 'C' signal carries the colour
- It would theoretically be possible to build a passive converter
to make composite from S-video (by adding the two signals together
with a couple of resistors), though I've never seen one, and it
wouldn't work wonderfully well.
However, I HAVE seen a converter (supplied with Hauppauge PCI cards)
which adapts a single RCA-phono connector for composite into
an S-video connector. This is purely a mechanical adaptor, connecting
to the 'Y' terminals on the S-video connector, and assumes that
you have configured the card appropriately. This type of converter
does not do any kind of signal conversion.
- SCART connectors provide 4 video input signals to the TV. In
normal use, these are composite plus R,G,B. When using RGB, the
composite signal is still present and used to provide syncs.
The TV will normally switch automatically between composite and RGB
under control of another signal ('fast blanking').
SCART connectors can also be used (with some TVs only) for S-video.
SCART to S-video adaptors are purely mechanical adaptors which
have no effect on the signals.
In this case, the 'Y' signal is fed on the composite pin on the
SCART connector, and 'C' on the red pin. There is nothing on the
connector itself to switch into S-video mode: it can only be used
if the TV has been manually configured to do S-video rather than
RGB. Many TVs don't accept S-video at all.
- You should be able to tell the difference between a b/w picture
due to wrong PAL/NTSC/SECAM selection and a b/w picture due to
connecting an S-video output to a composite input.
Look at a picture with some areas of solid colour.
If it's an S-video 'Y' signal, the vertical edges of coloured
areas will be just as sharp as the edges of black/white areas.
If it's a composite signal of the wrong type for the TV, the
edges of coloured areas should be noticeably fuzzy compared
to white areas which will be sharp. You may also be able to
see a 'grainy' appearance to areas that should be coloured
which is not visible in areas which are supposed to be grey.
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