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8-Bit MCUs

Windowed Watch Dog Timer (WWDT)

What is Windowed Watchdog Timer (WWDT)?

A WWDT acts as a system supervisor that ensures normal operation of the software. If the software execution takes longer or shorter than expected, the WWDT issues a Reset of the microcontroller. Windowed Watchdog Timer (WWDT) offers upper and lower time threshold whereas Watchdog Timer (WDT) offers only single threshold.

Why is WWDT Used?

Even after extensive tests and careful validation, an MCU can still get locked up while executing it’s program code. There are many reasons which can trigger this unexpected event including something as simple as temperature change or noise spike from the power supply. A proper implementation of the Watch Dog Timer can save the system from failure in these unfortunate cases acting as a last line of defense, by simply issuing a Reset of the microcontroller.

How does WWDT Work (in PIC and AVR MCU)?

The Windowed Watchdog Timer is a built in hardware module for most modern PIC and AVR MCUs. WWDT uses the internal oscillator as clock source and offers variable time-out period and window sizes. When the application starts, the WWDT starts counting to it’s pre-programmed time. User written code clears the WWDT within the pre-defined time window and the process starts over again. If the timer is not cleared during the pre-defined time window, then WWDT issues a Reset of the microcontroller.

windowed watch dog timer diagram