National Semiconductor Corporation

Erez Bar-Niv

Amos Intrater

Rafael Fried

A method and apparatus for waking up a computer system using a peripheral device connected to a standard parallel port of the computer system. Functionality is added to the parallel port Select line normally used to indicate that the peripheral device connected to the parallel port is on line when the select signal is high. A signal transition on the Select line from low to high is detected and used to wake up the computer system. This toggling of the Selected line is detected and used to activate the computer system power supply into a normal operating state from a power save state.

Method and apparatus for waking up a computer system via a parallel port

Reflections and cross talk in a high-speed, bidirectional transmission line are minimized by terminating the transmission line with a network including a 'serial' resistor connected in series between an end of the transmission line and a parallel (e.g. data) port, a 'pull-up' resistor connected to the transmission line side of the serial resistor, and a capacitor connected between the parallel port side of the serial resistor and ground. Optionally, a diode is connected between the pull-up resistor and a bias potential. A variety of exemplary values for these components (i.e., serial resistor, pull-up resistor, capacitor) are discussed, in the context of particular signals. Preferably, the capacitor and the resistors are positioned as close as possible to the connector.

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Raanana, Israel

Erez Bar-Niv