MEMORY PATCHING CIRCUIT

摘要

A read only memory (ROM) patching arrangement is disclosed for providing valid output information whenever ROM word locations containing invalid information are addressed. The disclosed arrangement uses a plurality of small capacity PROMs as a decoder to detect the receipt of each address word representing a defective ROM location. Upon each detection of a defective address, the decoder temporarily inhibits the output of the ROM and causes a small auxiliary memory to output valid program information as a substitute for that in the defective ROM location. A counter is used as a supplemental addressing source for both the decoder and the auxiliary memory. This increases the patching capability by subdividing the decoder and the auxiliary memory into 2n segments where n is the number of bits supplied by the counter.