Patent ID: 8099611

Claim:
A method of operating a powered communications interface of a power-sourcing equipment, the powered communications interface including coupling circuitry operative to couple data signals between the power-sourcing equipment and conductors of the cable, the method comprising: in a powered operating mode, supplying operating power to the powered device via the coupling circuitry in the form of a relatively high supply voltage across the conductors of the cable and a relatively high supply current through the conductors of the cable; and in a non-powered operating mode, (1) withholding the operating power from the powered device, and (2) applying a sequence of relatively low signaling voltages and relatively low signaling currents to the conductors of the cable via the coupling circuitry, the sequence of relatively low signaling voltages and currents including (a) first signaling voltages and currents of a detection and classification operation by which the presence and power requirements of the powered device are detected, and (b) second signaling voltages and currents by which the powered device provides additional information to the power-sourcing equipment, the additional information being encoded in the form of values and sequence of the second signaling currents conducted by the powered device in response to corresponding values and sequence of the second signaling voltages, wherein the power-sourcing equipment is provided with a control value indicating that the power-sourcing equipment is normally to withhold power even when the detection/classification operation indicates that the powered device is present; and wherein the additional information indicates the existence of a special operating condition of the powered device which should override the normal withholding of power; and wherein the powered operating mode is entered in response to receiving the additional information from the powered device.