IIRC, S-video
has 2 ground pins on the connector, and there's nothing to
stop them being commoned in the cable. Would that cuase a problem if
sucha a cable was used for ADB?
See
http://www.applefritter.com/node/9214 :
"Both ADB and S-Video cables use 4 pins, and are interchangeable.
Keep in mind that some S-Video cables are of higher quality than
ADB cables, so if you use an ADB cable for S-Video, the signal
may not be as good as if you used a proper S-Video cable."
"The only difference between an ADB cable and an SVideo cable is that
the ground pin and the shell are connected together on the ADB cable,
and the ground pin on an SVIDEO cable is not connected to the shell.
The only problem this causes is some devices don't detect the cable
being plugged in and won't switch to it."
I learnt long ago not to trust web sites as the definitive answer on
anything. Much of this sort of information is based on 'I've tried it and
it seems to work' without the author understanding the possible issues
involved.
For the case inquestion (ADB .vs. S-vide), yes, both cabls have 4 pin
mini-DIN on the ends. Both are straight-through wired. But there is a
very important difference. ADB has 4 distinct signals on the 4 pins
(IIRC, ground, +5V, data, power switch). S-video has 3 (Luminance,
Luminance ground, Chreomanance, Chromance ground). Most S-video cabels
are wired with the 4 pins being distict, but I can't think of anything
that prevents a cable from working as an S-video cable id the 2 grounds
arre linked inside the cable (I am pretty sure the S-video standard
implies the 2 grounds are linked inside each device). Whether any such
cables exist, I don't know, but I could easily see they would cuase
problems if used as an ADB cable.
-tony