Content-addressable memory with programmable field masking

Abstract

An apparatus and method for programmable field masking in content-addressable memory (CAM). The present invention provides a CAM with at least one group of memory cells interconnected by a word line and a match line. The group of memory cells includes data memory cells divided into a number of data memory cell fields for storing data bits of a data word. A mask memory cell is provided within the group of memory cells for storing at least one mask bit indicating a status of data stored in at least one of the data memory cell fields. The mask memory cell is operative to interrupt the match line in response to the stored mask bit. A match line detector detects a signal level on the match line to indicate if input data bits supplied on the data memory cell bit lines match data bits stored in at least one of the data fields. The data memory cell fields may be organized into a hierarchy, with mask memory cells connected between the data fields, to provide hierarchical masking. General programmable masking of any data field within the group is provided using multiplexed mask memory cells connected by bypass lines. The multiplexed mask memory cells may store one or more mask bits in order to allow a bypass line to be connected to portions of the match line, thereby masking a given data memory cell field.