A single chip microcomputer comprises a control circuit (12a, 12b), a processing circuit (13a, 13b) and a plurality of ad­dress register - status register pairs. A logical unit formed within the control circuit (12a, 12b) 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 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.