Abstract: An interface circuit can assign a common input/output port address to a plurality of I/O circuits. Each common I/O port is defined in terms of pages. In an actual data input/output, a specific port address is used for port control so as to select one common page. The interface circuit has a first decoder for decoding a specific port address signal. The interface circuit also had a data setter for setting data supplied from a specific bit line of the data bus. The data is set in the data setter in accordance with the decoded signal from the first decoder. Each of the plurality of I/O circuits has a second decoder for decoding the common I/O port address signal. An output from the setter enables a corresponding one of second decoders. As a result, a specific page is selected.