The SM3513 is a CMOS 4-bit single-chip microcomputer for databank incorporating data memory RAM, LCD driver (the output is adjustable in 16 steps for various contrast), key/switch input circuit, 8-bit parallel I/O port, 3 output ports, external memory control circuit, buzzer circuit and voltage detector circuit. One of three ports contains special output circuit for infrared (IR) communication. It is easy to realize timer function by timer signal interrupt since the oscillator circuit is built-in.