Modified universal serial bus interface implementing remote power up while permitting normal remote power down

摘要

A remote power key function is implemented between a remote input device having a power key and a host computer system using a four lead USB interface. Normal functioning of the USB interface and of the input device are not affected. An input device includes a remote logic circuit comprising a transistor, a diode, and a low voltage battery. The remote logic circuit and MPU receive a first input from the power key and battery and receives a second input from the host-computer provided power supply that is "1" if the host computer is powered-up, and is "0" otherwise. Remote logic circuit output is coupled to the D+ USB interface line, and MPU output is coupled to the D+ and D- interface lines. Clamping latch logic within the host computer has a first input that is the D+ line, and a second input that is the power supply "1" or "0" signal. Latch logic output is input to the latch input port of the host computer power supply. When the host computer is to be powered-down, the remote logic circuit first input causes the MPU to output a scan code recognized by the host computer as commanding a power-down condition.