Quote:
Originally Posted by Ghitulescu
To put an end to all wild speculations, the USB requires that a device is the Master and the other one is the Slave. This is hardwired, so if a device can connect to a PC (which by definition is a Master) it cannot connect to a Slave, via the same USB port. ...
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The signaling is hardwired, but the logic can be software controlled and adapt to conditions.
With USB (plain and simple) both the wiring and the logic are fixed. A device is either a Host (aka "master") or Client (aka "slave"), period.
With USB/OTG (a new and somewhat different animal) the logic is adaptable to the current condition and is controlled by the wiring. A USB/OTG device can operate as either a Master or Client. When used with a standard USB cable (all OTG devices currently use a microUSB 2.0 B connector) the device will work as a Client. When used with a special USB>OTG adapter or special USB>OTG device (e.g. certain memory sticks, ...) the device will will act as a Host. Currently, USB/OTG ports are found only on Tablets and tablet-esque smart phones. Devices running recent versions of Android provide full functionality in both modes. Tablets running Windows 8.1 provide full functionality in the Host mode but only act as a power consumer (read: they charge only) when in the Client mode; they don't act as a Mass Storage device for data transfer.