1. A control circuit, comprising: an external command recognition section for recognizing an external command, the external command being an operation command input from outside the control circuit; an internal ROM bank including a plurality of storage regions, the internal ROM bank being used to store an internal code for achieving operations specified by the external command recognized by the external command recognition section; an internal ROM selection section for selecting a required storage region from the plurality of storage regions of the internal ROM bank in accordance with the external command recognized by the external command recognition section; a program counter for selecting and indicating an address of an internal command to be executed from a plurality of addresses of internal commands stored in the Internal ROM bank; an internal command register for storing the internal command read from the internal ROM bank; and an internal command execution section for executing the internal command stored in the internal command register.