Importance

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Abstract

A content addressable memory (CAM) has a matrix of dual port memory cells each storing two encoded bits resulting from a data bit being combined with a mask bit. The encoded bits have differing values representing the data bit value when the cell is not masked and the same values when the cell is masked. During a CAM look-up operation when the encoded bits indicate the cell is not masked, a matching circuit of the cell compares the encoded bits and a reference bit so an output of the matching circuit indicates whether the data bit which resulted in the stored encoded bits is the same as the reference bit. When the cell is read by an address word and the encoded bits indicate the cell is not masked, the cell drives a read port with a level indicative of the data bit which resulted in the encoded bits. When the encoded bits indicate the cell is masked, the outputs of matching circuit and the read port are static.

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First Claim