| 摘要 |
A detector of an oscillation stopping, which detects the stopping of the oscillation of external clock 11, without increasing the load of CPU 45 in the micro computer 40, and generates a signal to reset the micro computer or exchanges the system clock from the external clock to an inner clock.In an embodiment, one shot pulse is generated for every standing up and/or down edge of the external clock. A capacitor of the charge-discharge circuit is charged and discharged at every one shot pulse. The voltage of the charge-discharge circuit is watched by a Schmitt circuit. When the voltage of the charge-discharge circuit exceeds a predetermined voltage, a signal for resetting the micro computer is generated.In another embodiment, an inner clock oscillation circuit, comprised of a ring oscillator, for example, is actuated, when the voltage of the charge/discharge circuit exceeds a predetermined voltage, and the system clock of the micro computer is exchanged to the inner clock from the external clock.In another embodiment, an interruption signal is sent to the CPU of the micro computer to execute an appropriate treatment after the stopping of the clock oscillation, when the voltage of the charge/discharge circuit exceeds a predetermined voltage.In another embodiment, a watchdog timer monitors the malfunction of the micro computer. It is judged whether the accident is a stopping of the oscillation of the clock or a malfunction of the micro computer. The treatment after the stopping of the clock is executed, according to the reason of the accident.
|
