US Patent 7193895 Redundant memory content substitution apparatus and method

A memory apparatus includes a main memory, a redundant memory, and a substitution control unit. The main memory is configured to receive a read address and output a main data word comprising a plurality of main data sub-words where the read address includes a first portion and a second portion. The redundant memory is configured to receive the read address first portion and output a redundant data sub-word. The substitution control unit includes a substitution control word memory configured to store a plurality of substitution control words and configured to receive the read address first portion and assert a substitution control word including a substitution address second portion. The read address first portion and substitution address second portion form a substitution address. The substitution control unit asserts a substitution control signal when there is a match between the read address and the substitution address.