What is a window watchdog timer?

Watchdog TimersFunction

A typical watchdog timer (WDT) detects abnormality and output a reset signal only when the periodical signal from the monitored MCU comes behind a certain time cycle or cease to come. Window WDTs, on the other hand, detect abnormality by sensing both the longer and shorter signaling cycles than the preset one. They are suitable for systems where high reliability is required.