US Patent No: 5,226,005

Number of patents in Portfolio can not be more than 2000

Dual ported content addressable memory cell and array

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Abstract

An improved CAM (content addressable memory) cell is provided with dual address lines operable independently for a Read operation or for a Write operation. The cell is additionally provided with dual ports so that the first port permits a data input for Write operations or alternatively a data input for Search-Compare operations. The second port (Data Output) is independently connected to enable Read out of data residing in the cell. Each CAM cell also has a coincidence line (match-hit) output to indicate when an input Search bit or word coincides with resident data within the CAM cell. The CAM cells are arranged in an array of "m" rows with each row having "n" bits to hold a "n" bit word. Operationally the array permits both "Read" and "Search-Compare" operations to be accomplished in one clock cycle rather than the usual requirement of 3-4 clock cycles.

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First Claim

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Patent Owner(s)

Patent OwnerAddressTotal Patents
UNISYS CORPORATIONBLUE BELL, PA2757

International Classification(s)

  • [Classification Symbol]
  • [Patents Count]

Inventor(s)

Inventor Name Address # of filed Patents Total Citations
Easley, Jeffery L Carlsbad, CA 2 77
Lee, David C Beaverton, OR 75 896
Malik, Ashgar K Escondido, CA 5 119

Cited Art

Patent Info (Count) # Cites Year
 
MITSUBISHI DENKI KABUSHIKI KAISHA (2)
5,111,427 Nonvolatile content-addressable memory and operating method therefor 70 1989
5,130,945 Content addressable memory combining match comparisons of a plurality of cells 19 1990
 
MASSACHUSETTS INSTITUTE OF TECHNOLOGY (1)
4,831,585 Four transistor cross-coupled bitline content addressable memory 21 1987
 
VERIZON LABORATORIES INC. (1)
4,862,412 Content-addressable memory having control circuitry and independent controls for match and write cycles 19 1988
 
OTHER [CHECK PATENT PROFILE FOR ASSIGNMENT INFORMATION] (1)
4,779,226 Complementary high performance cam cell 25 1986

Patent Citation Ranking

Forward Cites

Patent Info (Count) # Cites Year
 
NETLOGIC MICROSYSTEMS, INC. (29)
6,122,706 Dual-port content addressable memory 5 1993
5,452,243 Fully static CAM cells with low write power and methods of matching and writing to the same 15 1994
6,148,364 Method and apparatus for cascading content addressable memory devices 107 1997
6,240,485 Method and apparatus for implementing a learn instruction in a depth cascaded content addressable memory system 54 1998
6,219,748 Method and apparatus for implementing a learn instruction in a content addressable memory device 49 1998
6,381,673 Method and apparatus for performing a read next highest priority match instruction in a content addressable memory device 30 1998
6,418,042 Ternary content addressable memory with compare operand selected according to mask value 33 1998
6,137,707 Method and apparatus for simultaneously performing a plurality of compare operations in content addressable memory device 101 1999
6,460,112 Method and apparatus for determining a longest prefix match in a content addressable memory device 38 1999
7,143,231 Method and apparatus for performing packet classification for policy-based packet routing 8 1999
6,539,455 Method and apparatus for determining an exact match in a ternary content addressable memory device 34 1999
6,499,081 Method and apparatus for determining a longest prefix match in a segmented content addressable memory device 50 1999
6,154,384 Ternary content addressable memory cell 113 1999
7,487,200 Method and apparatus for performing priority encoding in a segmented classification system 3 2000
6,697,911 Synchronous content addressable memory 11 2001
7,110,407 Method and apparatus for performing priority encoding in a segmented classification system using enable signals 5 2001
7,110,408 Method and apparatus for selecting a most signficant priority number for a device using a partitioned priority index table 3 2001
6,567,340 Memory storage cell based array of counters 20 2001
6,480,406 Content addressable memory cell 34 2001
6,944,709 Content addressable memory with block-programmable mask write mode, word width and priority 34 2001
6,934,795 Content addressable memory with programmable word width and programmable priority 37 2001
6,564,289 Method and apparatus for performing a read next highest priority match instruction in a content addressable memory device 21 2001
6,892,272 Method and apparatus for determining a longest prefix match in a content addressable memory device 8 2002
6,574,702 Method and apparatus for determining an exact match in a content addressable memory device 22 2002
6,678,786 Timing execution of compare instructions in a synchronous content addressable memory 14 2002
6,845,025 Word line driver circuit for a content addressable memory 13 2003
6,961,810 Synchronous content addressable memory 4 2003
7,272,027 Priority circuit for content addressable memory 1 2004
7,246,198 Content addressable memory with programmable word width and programmable priority 9 2005
 
INTERNATIONAL BUSINESS MACHINES CORPORATION (8)
5,396,449 Fast content addressable memory with reduced power consumption 48 1993
5,668,972 Method and system for efficient miss sequence cache line allocation utilizing an allocation control cell state to enable a selected match line 22 1994
6,161,164 Content addressable memory accessed by the sum of two operands 4 1996
6,353,558 Method and apparatus for writing to memory cells 2 2000
6,487,101 Use of search lines as global bitlines in a cam design 11 2001
7,120,732 Content addressable memory structure 4 2004
7,337,268 Content addressable memory structure 0 2006
7,464,217 Design structure for content addressable memory 0 2007
 
ALTERA CORPORATION (4)
6,144,573 Programmable logic devices with improved content addressable memory capabilities 22 1999
6,344,989 Programmable logic devices with improved content addressable memory capabilities 7 2000
7,111,110 Versatile RAM for programmable logic device 10 2002
7,480,763 Versatile RAM for a programmable logic device 0 2006
 
CORE NETWORKS LLC (4)
6,339,539 Content addressable memory having read/write capabilities that do not interrupt continuous search cycles 23 2000
6,553,453 Variable width content addressable memory device for searching variable width data 21 2000
RE41659 Methods and circuitry for built-in self-testing of content addressable memories 0 2005
RE41992 Methods and circuitry for built-in self-testing of content addressable memories 0 2006
 
SANDISK CORPORATION (3)
6,317,349 Non-volatile content addressable memory 35 1999
6,166,938 Data encoding for content addressable memories 42 1999
6,157,558 Content addressable memory cell and array architectures having low transistor counts 35 1999
 
INTEL CORPORATION (2)
6,421,289 Method and apparatus for charge-transfer pre-sensing 4 2000
7,013,367 Caching associative memory using non-overlapping data 1 2003
 
INTERGRAPH HARDWARE TECHNOLOGIES COMPANY (2)
5,546,569 Apparatus for writing data to and reading data from a multi-port RAM in a single clock cycle 19 1993
5,598,115 Comparator cell for use in a content addressable memory 74 1995
 
UNISYS CORPORATION (2)
5,420,993 Extended address translation system for pointer updating in paged memory systems 16 1994
5,673,415 High speed two-port interface unit where read commands suspend partially executed write commands 14 1996
 
CSELT - CENTRO STUDI E LABORATORI TELECOMUNICAZIONI S.P.A. (1)
6,169,685 Content addressable memories 18 2000
 
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. (1)
6,163,473 Memory for storing encoded mask and data bits 12 2000
 
KABUSHIKI KAISHA TOSHIBA (1)
5,504,870 Branch prediction device enabling simultaneous access to a content-addressed memory for retrieval and registration 7 1995
 
MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. (1)
7,289,345 CAM circuit and output method thereof 0 2004
 
MITSUBISHI DENKI KABUSHIKI KAISHA (1)
5,339,268 Content addressable memory cell and content addressable memory circuit for implementing a least recently used algorithm 51 1992
 
MUSIC SEMICONDUCTORS, INC. (1)
5,383,146 Memory with CAM and RAM partitions 128 1992
 
NEC ELECTRONICS CORPORATION (1)
5,933,363 Associative memory having comparator for detecting data match signal 16 1998
 
OKI SEMICONDUCTOR CO., LTD. (1)
5,313,436 Address transition detecting circuit 3 1992
 
TELEFONAKTIEBOLAGET LM ERICSSON (PUBL) (1)
6,259,620 Multiple entry matching in a content addressable memory 6 2000
 
TRACE STEP HOLDINGS, LLC (1)
6,751,111 High density memory cell 9 2002
 
OTHER [CHECK PATENT PROFILE FOR ASSIGNMENT INFORMATION] (1)
6,510,069 Content addressable memory apparatus and method of operating the same 5 2001