The M66222 is a mail box that incorporates two complete CMOS shared memory cells of 128 x 8 -bit configuration using highperformance silicon gate CMOS process technology, and are equipped with two access ports of A and B. Access ports A and B are equipped with independent addresses CS, WE and OE control pins and I/O pins to allow independent and asynchronous read/write operations individually. This product exclusively performs a write operation from A port and a read operation from B port for one memory, and a read operation from A port and a write operation from B port for the other memory.