The 4551 Group is a 4-bit single-chip microcomputer designed with CMOS technology. Its CPU is that of the 4500 series using a simple, high-speed instruction set. The computer is equipped with an 8-bit timer with a reload register, a 14-bit timer which is also used as a watchdog timer, a 4-bit timer with a reload register, a carrier wave output circuit and an LCD control circuit. The mask ROM version and built-in PROM version of 4551 Group are produced as shown in the table below.