The M66008 is a semiconductor integrated circuit providing the 16-bit serial input-parallel output and parallel input-serial output shift register function. Independent built-in registers for serial input-parallel output and parallel input-serial output enable serial input data to be read into a shift register during output of serial data converted from parallel data. In addition, parallel data input/output pin can be placed in input or output mode in bits. The M66008 is widely applicable to I/O port extension for MCU, data communication of serial bus system, etc. FEATURES