ONE-CHIP MICROCOMPUTER

PURPOSE:To suppress a chip area small by performing the operation of a RAM for storing the arithmetic result of a CPU or the like also by a ROM using an electric erase and write enable nonvolatile memory. CONSTITUTION:A flash EEPROM is used for a ROM 20, a read control signal from a CPU 10 is outputted through a control signal line 3c to a control circuit 4c, a read address is outputted to an address bus 1, a series of operations for fetching an instruction from this address of the ROM 20 through a data bus 2 and executing it are repeated, on the other hand, when storing the arithmetic result of the CPU 10, a write control signal and a designating signal for an area to be erased are outputted through a control signal line 3d to a control circuit 4d, the designated area is erased, and the arithmetic result of the CPU 10 is stored.