PURPOSE: To attain ease of processing of a microcomputer by adopting serial form for transmission/reception of a data to/from the microcomputer so as to minimize the number of interfaces in comparison with that of a parallel form and counting a clock signal so as to decode generation of an instruction in the inside of the titled device.

CONSTITUTION: An instruction decoding section 2 samples a command signal 3 given from an external part of the device by using a reference pulse signal 4 generated from a clock generating part 1 to generate a command A data storage part 6 consists of a serial register and an address generating circuit. The serial register is shifted by a transfer clock 8 in the unit of one bit, stores the data from an input/output serial register and outputs the data to the external side of the device. The data stored in the data storage section 6 is transferred to a data processing part 9 via an internal bus 10 and a write data is transferred from the data processing section 9 to the data storage part 6.