Powered communications interface providing low-speed communications between power-sourcing equipment and powered device in non-powered operating mode

摘要

A powered communications interface in a power-over-Ethernet (POE) system has a non-powered operating mode in which it withholds operating power from a powered device and applies relatively low signaling voltages and currents to the conductors of the Ethernet cable which include (a) first signaling voltages and currents of a detection/classification operation, and (b) second signaling voltages and currents of a low-speed communications operation by which the power-sourcing equipment and the powered device exchange operational information. The low-speed communications from the power-sourcing equipment to the powered device are conveyed by values and sequencing of the second signaling voltages, and low-speed communications from the powered device to the power-sourcing equipment are conveyed by values and sequencing of the second signaling currents conducted by the powered device in response to the second signaling voltages from the power-sourcing equipment. Frame-based communications protocols or lookup-table-based communications may be used.