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Cascading content addressable memory devices with programmable input/output connections

  • US 7,043,600 B2
  • Filed: 05/12/2003
  • Issued: 05/09/2006
  • Est. Priority Date: 05/12/2003
  • Status: Expired due to Term
First Claim
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1. A CAM system for generating an output on a bus in response to a key, the CAM system comprising:

  • at least two clusters that each include M CAM devices, wherein each CAM device has a priority N within the cluster to which it belongs, where N ranges from 1 to M, and each CAM device includes;

    i) a CAM array configured to hold entries and to determine if each entry matches the key;

    ii) (M−

    1) disable connections, where the CAM device of priority N has (N−

    1) of the disable connections programmed as inputs configured to receive disable-in signals from the (N−

    1) higher-priority CAM devices within the cluster, and has the remaining (M−

    N) disable connections programmed as outputs configured to provide a disable-out signal to the (M−

    N) lower-priority CAM devices within the cluster; and

    iii) a cascade circuit configured to disable the CAM device from driving the output onto the bus when any of the disable-in signals received by the CAM device are asserted; and

    a controller configured to receive a cluster-match signal from the clusters and to generate a cluster-disable signal for the clusters, wherein the cluster-disable signal for a particular cluster is asserted when any cluster-match signal received by the controller from any cluster having higher priority than that particular cluster is asserted;

    wherein each CAM device further includes a connection configured to receive the cluster-disable signal for the cluster containing the CAM device and a connection configured to provide the cluster-match signal for that cluster; and

    wherein each cascade circuit is further configured to disable the CAM device from driving the output onto the bus when the cluster-disable signal is asserted.

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