If a region designated by an address signal is a logic control region, an interface portion transmits/receives data to/from a register instead of a DRAM. A data signal used at that time is a control command for a logic circuit held in the register or input data for a process in the logic circuit. Depending on the content held in the register, the logic circuit performs, for example, an encryption process or a process which takes for a microcomputer a long time to complete such as an image processing. The result of processing is stored in the register and read in a sequence of reading from the DRAM.