MICROPROCESSOR

摘要

PURPOSE: To operate a microprocessor with a clock signal having a wide frequency band. CONSTITUTION: The clock signal 9 generated by a clock generating circuit 1 in normal operation is inputted to the PLL multiple oscillating circuit 4 of the microprocessor 3 and a selecting circuit 5 selects the output of the PLL multiple oscillating circuit 4. A microprocessor core 8 operates with a multiplied operation clock signal 14. To place the microprocessor 3 in operation at a clock frequency exceeding the clock input frequency band that the PLL multiple oscillating circuit 4 can follows up, the selecting circuit 5 is switched from the side of a PLL multiplying circuit 4 to a low-speed clock signal with the clock switching signal 13 from a clock control circuit 7.