Importance

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Abstract

In a system that has a redundant pair of modules where one module is the active module and the other module is the standby module, each of the two modules includes equipment such as an inexpensive programmable logic device to provide a protection switching algorithm for determining, at the individual module level, whether a module is in the active or standby state and switching a module from a standby state to its active state when the module in the active state becomes defective. The number of wires that are required as module to module indicators is reduced to two. The processor can make the active, standby determination when the two modules are powered up simultaneously, when one module is inserted subsequent to the other, or where a module has been active and then fails or is unexpectedly removed.

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First Claim