The M66006 is a semiconductor integrated circuit which has 12-bit shift register function to execute serial-parallel conversion and parallel-serial conversion. Because a serial-parallel shift register and a parallel-serial shift register are independently built in this IC, it is possible to read serial input data to a shift register while converting parallel data into serial data. Also, parallel data I/O pins can be set to input mode or output mode bit-by-bit. The M66006 can be widely used for I/O port expansion of MCU, serial bus system data communication, etc.