A content addressable memory (CAM) has a matrix of dual port memory cells each storing two encoded bits resulting from a data bit being combined with a mask bit. The encoded bits have differing values representing the data bit value when the cell is not masked and the same values when the cell is masked....http://www.google.com.tw/patents/US6163473?utm_source=gb-gplus-share專利 US6163473 - Memory for storing encoded mask and data bits
