US 5,689,202 AGranted

Integrated circuit for automatic determination of PCI signaling environment--either 3.3V or 5V

AssigneeHewlett-Packard Company

InventorCheryl A. Ranson

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Abstract

An integrated circuit automatically detects a Peripheral Component Interconnect signaling environment, which may be based on either a first voltage or a second voltage, and matches output voltage and output current characteristics of an output signal with Peripheral Component Interconnect signal specifications. The integrated circuit includes a signaling environment detection circuit and an output driver circuit. The signaling environment detection circuit compares an integrated circuit supply voltage with a reference voltage, whose value is between the first voltage and the second voltage, and generates a detected environment signal representative of the signaling environment. The output driver circuit adjusts the output voltage and output current of the output signal to match the Peripheral Component Interconnect signal specifications based on the detected environment signal by sourcing additional current to the output pad to match the Peripheral Component Interconnect signal specifications when the detected environment signal indicates a signaling environment based on the first voltage, and sinking additional current from the output pad to match the Peripheral Component Interconnect signal specifications when the detected environment signal indicates a signaling environment based on the second voltage.

An integrated Circuit for automatically detecting a Peripheral Component Interconnect signaling environment and for matching output voltage and output current characteristics of an output pad signal of the integrated circuit with Peripheral Component Interconnect signal specifications, the signaling environment being based on either a first voltage or a second voltage, the integrated circuit comprising:

a signaling environment detection circuit connected to receive an integrated circuit supply voltage and a reference voltage, wherein the reference voltage represents a nominal value between the first voltage and the second voltage, to compare the integrated circuit supply voltage with the reference voltage and to produce a detected environment signal representative of the signaling environment;
and
an output driver circuit connected to receive the detected environment signal for producing a pullup signal on an output pad when the output driver circuit is enabled to drive the output pad to a logical high state, and for producing a pulldown signal on the output pad when the output driver circuit is enabled to drive the output pad to a logical low state;
wherein the output driver circuit comprises an output characteristics adjustment circuit for adjusting the output voltage and output current of the output pad signal to match the Peripheral Component Interconnect signal specifications based on the detected environment signal,
the output characteristics adjustment circuit comprising an extra-pullup circuit and an extra-pulldown circuit, wherein the extra-pullup circuit is connected to be enabled by the pullup signal and is connected to receive the detected environment signal to source additional current to the output pad to match the Peripheral Component Interconnect signal specifications when the detected environment signal indicates that the signaling environment is based on the first voltage, and wherein the extra-pulldown circuit is connected to be enabled by the pulldown signal and is connected to receive the detected environment signal to sink additional current from the output pad to match the Peripheral Component Interconnect signal specifications when the detected environment signal indicates that the signaling environment is based on the second voltage.

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Abstract

Claims11