| 摘要 |
PURPOSE: A frequency detection unit is provided, which prevents a frequency detection operation of a clock signal from being controlled by a physical operation, and also prevent a random circuit change by a hacking. CONSTITUTION: A divider unit(10) divides an inputted clock signal(CLK), and a multiplexer(MUX) outputs the clock signal and a clock signal(CLK) divided by the divider unit according to a set signal selectively. A detection unit(20) detects a frequency of the clock signal being output selectively by the multiplexer. A mode control unit outputs the set signal according to an output signal(OUT) of the detection unit. And an output control unit outputs the detection result of the detection unit according to the set signal of the mode control unit.
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