Content addressable memory with flag storage to indicate memory state

Claim 1

A content addressable memory (CAM) device for performing a retrieving operation based upon given retrieval data and for designating a specified word or word group, comprising: a CAM cell array (2) for storing data therein, a predetermined column (2) within said array (2) forming a flag storing means; first input/output control means (1) for entering write data to said CAM cell array (2) and for outputting read data from said CAM memory cell array (2), with a particular timing; second input/output control means (11) for entering a flag signal to said predetermined column (12) of said CAM cell array (2), with timing thereof controlled in common with said particular timing of said first input/output control means (1); said flag storing means (12) receiving from the second input/output control means (11) and storing a flag signal indicating whether each word in the CAM cell array (2) is in a data written state or in an empty state and for undergoing retrieval by said first and second input/output control means (1), (11); reset means (11) for writing a flag signal indicating an empty state for all words of said flag storing means (12); empty word retrieving means (1, 3, 11) for detecting an empty word by making a retrieval in said flag storing means (12) by the flag signal from said second input/output controls means (11); data writing means (1, 11) for writing in an empty word of said CAM cell array (2) the data from said first input/output control means (1) and for simultaneously writing in the corresponding portion of said flag storing means (12) the flag signal indicating the data written state from said second input/output control means (11); specified word retrieving means (1, 3, 11) for detecting a specified word by making a retrieval in said CAM cell array (2) with retrieval data from said first input/output control means (1) and simultaneously making a retrieval in said flag storing means with the flag signal from said second input/output control means (11).

Claim 8

A method for operating a content addressable memory (CAM) device for performing a retrieving operation based upon given retrieval data and for designating a specified word or word group, wherein said CAM device comprises: a CAM cell array (2) for storing data therein, a predetermined column (12) within said CAM cell array (2) forming a flag storing means; first input/output control means (1) for entering write data to said CAM cell array (2) and for outputting read data from said CAM cell array (2) with a particular timing; and second input/output control means (11) for entering a flag signal to said predetermined column (12) of said CAM cell array (2) with timing thereof controlled in common with said particular timing of said first input/output control means (1); said flag storing means receiving from said second input/output control means (11) and storing a flag signal indicating whether each word in said CAM cell array (2) is in a data written state or in an empty state and for undergoing retrieval by said first and second input/output control means (1), (11); said method for operating said CAM device, comprising the steps of: writing a flag signal indicating an empty state for all words in said flag storing means (12) for resetting; detecting an empty word by making a retrieval in said flag storing means (12) with the flag signal from said second input/output control means (11); writing in an empty word of said CAM cell array (2) the write data from said first input/output control means (1) and simultaneously writing in a corresponding portion of said flag storing means (12) the flag signal indicating a data written state; and detecting a specified word by making a retrieval in said CAM cell array (2) with retrieval data from said first input/output control means (1) and simultaneously making a retrieval in said flag storing means (12) with the flag signal from said second input/output control means (11).

Claim 9

A method for operating a content addressable memory (CAM) device for performing a retrieving operation based upon given retrieval data and for designating a specified word or word group, wherein said CAM device comprises: a CAM cell array (2) for storing data therein, a predetermined column (12) within said CAM cell array (2) forming a flag storing means; first input/output control means (1) for entering write data to said CAM cell array (2) and for outputting read data from said CAM cell array (2) with a particular timing; and second input/output control means (11) for entering a flag signal to said predetermined column (12) of said CAM cell array (2) with timing thereof controlled in common with said particular timing of said first input/output control means (1); said flag storing means receiving from said second input/output control means (11) and storing a flag signal indicating whether each word in said CAM cell array (2) is in a data written state or in an empty state and for undergoing retrieval by said first and second input/output control means (1), (11); said method for operating said CAM device, comprising the steps of: writing a flag signal indicating an empty state for all words in said flag storing means (12) for resetting; detecting an empty word by making a retrieval in said flag storing means (12) with the flag signal from said second input/output control means (11); writing in an empty word of said CAM cell array (2) the write data from said first input/output control means (1) and simultaneously writing in a corresponding portion of said flag storing means (12) the flag signal indicating a data written state; and detecting a specified word by making a retrieval in said CAM cell array (2) with retrieval data from said first input/output control means (1) and simultaneously making a retrieval in said flag storing means (12) with the flag signal from said second input/output control means (11).