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Dual Port USB Devices

These are usually some form of disk drive (but may be a "cable-powered" hub):





The form of their connection cable presumes that more power (current) is available when they are connected to two USB ports. Whilst this appears to be correct for laptop or netbook USB ports which, presumably, have active current limiting1 circuitry, this seems not to be so for many powered hubs. Observations of the above devices behaviour2 and measurements of inter-port connectivity tend to confirm this. The latter shows that, for most devices3, the power connections of the output ports are connected in parallel and, hence, it will be the current loading and/or limiting behaviour of the hub's PSU that is important.

  1. Probably upto 500mA - the maximum specified single USB port load (1)

  2. Failure to mount or Partion Block Corruption (2)

  3. Such as those based upon the Genesys Logic, Inc (ID 05e3:0608) chipset (3)

2018-06-16 20:20