Glossary · Watchdog
What is Watchdog timer?
A timer in the controller firmware that stops execution and raises a fault if one scan takes longer than allowed.
It means any loop that fails to end inside a scan will drop the controller to STOP. So never write a WHILE whose condition may never become false, and never run an unbounded FOR.
Heavy work is spread across scans or moved to a lower-priority task. The lab on this site simulates the same thing: it aborts after 10000 iterations in one scan.
Related terms
- Scan cycle
- The loop a PLC repeats thousands of times a minute: read the inputs, run the program top to bottom, write the outputs.
- Task
- The scheduling unit in a controller: which programs run, how often, and at what priority.