Browse Prior Art Database

Individually Maskable Content Addressable Memory Cell

IP.com Disclosure Number: IPCOM000114974D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Dietz, CD: AUTHOR

Abstract

Disclosed is a new type of Content Addressable Memory (CAM) cell which allows programmable control over which bits in the CAM array participate in the CAM lookup (comparison).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 71% of the total text.

Individually Maskable Content Addressable Memory Cell

      Disclosed is a new type of Content Addressable Memory (CAM)
cell which allows programmable control over which bits in the CAM
array participate in the CAM lookup (comparison).

      Fig. 1 shows two typical CAM cells.  Conventional CAM arrays
use these types of CAM cells to prevent certain rows or columns of
the CAM array from participating in the CAM lookup.  The Individually
Maskable Content Addressable Memory (IMCAM) cell, however, allows
complete programmable control over which individual bits in the CAM
array participate in the CAM lookup.

      Fig. 2 shows an IMCAM cell.  The IMCAM cell consists of a CAM
cell, which holds the compare data, and a RAM cell, which holds a
mask bit.  Setting the mask bit to a zero value allows the comparator
in the CAM cell to discharge the MATCH line.  Setting the mask bit to
a one value, however, disables the comparator in the CAM cell,
preventing it from discharging the MATCH line.  Thus, building CAM
arrays with the IMCAM cell yields a CAM array whose every bit can be
individually masked from the CAM lookup.

      Fig. 2 shows only one implementation of the IMCAM cell.  The
IMCAM cell's function can be implemented in many ways.  For example,
if a CAM array designer wishes the CAM lookup to be controlled by the
arrival of the CAM search data (Fig. 1B), no enable signal is needed,
and the NOR gate shown in Fig. 2 can be eliminated, allowing the CAM
d...