A typical single chip microcomputer disclosed in the present application comprises a control circuit, a processing circuit and a plurality of address register--status register pairs. A logical unit formed within the control circuit comprises an electrically writable non-volatile-semiconductor memory device. Information can be externally written into the non-volatile semiconductor memory included in the logical unit, and the above described plurality of address register--status register pairs can be arbitrarily selected. As a result, logic function of the logical unit can be arbitrarily established in accordance with externally supplied information. Demanded specifications of various users can be satisfied by the logic function thus arbitrarily formed.