| 摘要 |
PURPOSE: A circuit and a method for switching a clock of an MCU(Micro Controller Unit) are provided to prevent a failure of entire system by resetting the system after replacing a system clock occurring breakage by a noise with an internal clock. CONSTITUTION: A clock signal input part(16) inputs an external system clock signal to the MCU(100). A reset signal input part(17) inputs a reset signal. An internal RC oscillator(14) replaces the external system clock broken by the noise. A noise detecting circuit(13) detects that the external system clock is broken by the noise. A clock signal selector(12) inputs the system clock inputted through the clock signal input part to a CPU(10) if no detection signal is inputted from the noise detecting circuit, and inputs the clock signal of the internal RC oscillator to the CPU if the noise is detected by the noise detecting circuit. A watchdog counter(11) outputs a watchdog reset signal by executing a counter operation if the clock signal selector inputs the clock signal of the internal RC oscillator to the CPU. A reset signal input part(17) inputs the system reset signal to the CPU by executing an OR operation with the watchdog reset signal.
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