PURPOSE: To provide a microprocessor which can gain synchronous access to an external memory without reference to whether the external memory operates at the same frequency as the operating frequency of the microprocessor or at a frequency a half as high as the microprocessor operating frequency.

CONSTITUTION: The microprocessor 16 includes speed control input 30 for receiving a speed control signal having a 1st level representing the same microprocessor frequency equal to the external memory frequency 14 or a 2nd level representing a microprocessor frequency twice as high as the external memory frequency 14. Memory access control is coupled with the speed control input and allows access to the external memory in synchronism with an external memory clock 14 in response to a speed control signal, an internal microprocessor clock, and the external memory clock 14 when the external memory frequency is equal to or a half as high as the microprocessor frequency.