Glossary
What is Task?
The scheduling unit in a controller: which programs run, how often, and at what priority.
A cyclic task runs its program at a fixed interval, say 10 ms for fast control and 100 ms for communications and reporting. An event task runs on an interrupt.
Splitting programs across tasks with different intervals is the proper way to keep scan time stable: critical logic fast, everything else slower.
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.
- Watchdog timer
- A timer in the controller firmware that stops execution and raises a fault if one scan takes longer than allowed.
- PROGRAM
- The top program organization unit: bound to a task, executed cyclically, and keeping its variables between scans.