AN5757S Datasheet | Panasonic

Overview Microcontrollers are often used in harsh environments where power supply transients, electromagnetic interference (EMI), and electrostatic discharge (ESD) are abundant. Program corruption caused by bus corruption and electromagnetic discharges can cause a microprocessor to execute erroneous instructions. In these environments, a watchdog timer is a useful peripheral that can help catch and reset a microcontroller that has gone "out of control." A watchdog timer is a simple countdown timer which is used to reset a microprocessor after a specific interval of time. In a properly operating system, software will periodically "pet" or restart the watchdog timer. After being restarted, the watchdog will begin timing another predetermined interval. When software or the device is not functioning correctly, software will not restart the watchdog timer before it times out. When the watchdog timer times out, it will cause a reset of the microcontroller. If the system software has been designed correctly and there has been no hardware failure, the reset will cause the system to operate properly again. The reset condition must be a "safe" state. For instance, it would not be wise to have the reset state of a magnetic stripe card reader enabling the write head. Many systems have been designed using an external watchdog timer. The Secure Microcontroller family eliminates the need for external ponents by incorporating an internal watchdog timer. By moving the watchdog timer inside the microcontroller, the number of devices in the system is reduced, increasing the overall system reliability. The watchdog timer can take advantage of the high-precision crystal oscillator used by the microcontroller, rather than the imprecise RC oscillator used by most independent watchdog timers. The operation of the watchdog timer is independent of the microcontroller, unless specifically addressed via the Timed Access procedure. The possibility of an out-of-control microcontroller...