Fons Adriaensen wrote:
>On Sat, Dec 31, 2016 at 07:10:16AM +0100, Clemens Ladisch wrote:
>> The two data lines (D+ and D-) have controlled impedances and drive
>> levels so that the effective currents are symmetrical, but when both
>> lines are pulled low to signal EOP, there is not necessarily an equivalent
>> return current over the ground line.
>
>There must be. The net sum of the currents flowing through he cable
>must be zero, unless some current takes a path (e.g. via protective
>ground) not going via the cable.
>
>If two devices are connected only by the USB cable there is no
>such path.
Indeed. But if the device is _not_ bus powered, there is such a path.
Regards,
Clemens
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Received on Sat Dec 31 16:15:02 2016
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