On Sat, Sep 29, 2001 at 03:54:30AM -0700, Sami YOUSIF wrote:
> I have seem some "noname" so called "active" cables that do not have the
> correct grounding/wiring/distance requirements.
>
> Also... since many "active cables" do not have their own power, they can
> only work to extend low power devices or devices with their own power.
> {which is also where grounding becomes an issue}
They could have a DC-DC converter built in to bump up the output
voltage. They usually just have thicker (more copper, less voltage drop)
power lines in the cable, though.
The length is with digital repeating not a problem.
Now the grounding. What are the requirements?
> Most models are actually mini hubs (thats what the chip/kink/bulky header on
> one side of the cable does) but most users forget or are unaware of the max
> 4 hubs rule...
The problem is that they are not hubs.
> so if you have a Keyboard that has an extra port on it [which means that it
> has a built in hub as well; examples are some sony USB keyboards are
> detected as a four device hub, with 3 ports used], and use an active
> extension cable. the usb mouse connected to that keyboard port is actually
> on the "third" hub in the chain... which means that it can "break" if the
> extenstion cable is not connected to the root hub...
The problem seen by me also appears without any hubs present.
>
> most users do not realize the regulations on USB devices and so
> manufacturers of the "regular" devices are the ones blamed when their device
> fails to work when an extenstion cable is used... [which is why it seems
> that some device manufacturers will only troubleshoot their devices if the
> only items on the chain are their OWN hubs or connected to the root hubs]
> ...
--
Vojtech Pavlik
SuSE Labs
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