What is a watchdog timer?

The Watchdog Timer (WDT) is a component of the microcontroller and plays an important role in the debugging and running of the microcontroller program. Its main function is to reset the microcontroller by resetting the device (if the software does not clear the device) when a software failure occurs. It can also be used to wake up the device from sleep or idle mode.

Working Principle of Watchdog Timer

When enabled, the WDT will increment until it overflows, or “times out.” A WDT time-out forces a device Reset, unless the device is in Sleep or Idle mode. To avoid a WDT time-out Reset, the user must periodically clear the Watchdog Timer using the PWRSAV or CLRWDT instructions. If the WDT times out during Sleep or Idle mode, the device wakes up and continues code execution from the point where the PWRSAV instruction was executed. In both cases, the WDTO bit (RCON<4>) is set, indicating that the device Reset or wake-up event was caused by a WDT time-out. If the WDT wakes the CPU from Sleep or Idle mode, the Sleep status bit (RCON<3>) or Idle status bit (RCON<2>) is also set, indicating that the device was previously in a power-saving mode.

Watchdog timer function

The watchdog timer (WDT) is a component of the microcontroller and is important in the debugging and running of the microcontroller program. Its main function is to reset the microcontroller by resetting the device (if the software does not clear the device) when a software failure occurs. It can also be used to reset the device from sleep or idle mode. The watchdog timer provides an independent protection system for the microcontroller. When the system fails, after the optional timeout period, the watchdog will respond with a RESET signal. For example, the x25045 has three optional timeout periods of 1.4 seconds, 600 milliseconds, and 200 milliseconds. When your program crashes, the x25045 will reset the microcontroller.

Most watchdog timer ICs generate a single, limited output pulse of limited duration when the watchdog times out. This is suitable for triggering a reset or interrupting a microprocessor, but some applications require a latched output (fault indicator).

Considering safety issues, automotive electronic systems need monitoring circuits to monitor fault tolerance or safety. The watchdog timer is an ideal way to meet such requirements. It detects the failure status of the circuit or ?C by detecting the periodic pulses generated by the microcontroller under normal working conditions. Once a failure occurs, it can immediately switch to the backup/redundant system. > Operation of the watchdog timer

During normal operation, a WDT time-out will generate a device reset. If the device is in sleep mode, a WDT time-out will wake up the device and continue normal operation (called WDT wake-up). Clearing the WDTE bit to 0 will permanently disable the WDT.

The postscaler assignment is completely software controlled, meaning it can be changed at any time during program execution.

To avoid an unpredictable device Reset, the following instruction sequence must be executed when changing from the Timer0 prescaler assignment to the WDT postscaler assignment. This instruction sequence must be executed even if the WDT is disabled.