PURPOSE: To enable an 8-bit or 16-bit MPU to a easily perform the bus control against an optional MPU by using a means which sets two types of action modes for single use and two types of action modes for parallel use of 2 pieces with switching performed among those modes.

CONSTITUTION: An interface (a) is secured to an MPU 31a of an 8-bit exclusive bus type of a Z80 system. An address bus (16 bits) and a data bus (8 bits) of the MPU 31a are connected to an address exclusive input terminal and an address data common input/output terminal respectively. An MPU interface part 1 knows the action mode from a fact that the action mode signal received from a mode switching terminal is equal to 00, for example, and performs the parallel transfer control of the address signal and data signal between a bus of the MPU and an internal system bus. An 8-bit shared bus type (b) of an 8085 system is prepared together with a 16-bit exclusive bus type (c) of a 6800 system, and a 16-bit shared bus type (d) of the 8085 system respectively.