Wanted: Apple ADB keyboard

Tony Duell ard at p850ug1.demon.co.uk
Tue Jun 19 14:38:58 CDT 2007


> >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



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