Glossary · Automation fundamentals, platforms and components
Task
Also known as: PLC task, Cyclic task
German: Task
In IEC 61131-3, a task is an execution control element that triggers the execution of programs or function blocks, either cyclically at a set interval or when an event occurs, with an assigned priority.
- Automation components
In one sentence
In IEC 61131-3, a task triggers programs cyclically or on events with an assigned priority, defining when and how often code runs.
Example
The motion task runs every 2 ms with high priority, while the HMI communication task runs every 100 ms with low priority.
How it applies
- Engineering: Assign time-critical functions to fast, high-priority tasks and background work to slower ones. Data shared between tasks needs consistent access, because a higher-priority task can interrupt a lower one mid-cycle.
- Commissioning: Monitor execution time and cycle overruns per task; a task Watchdog detects when a task exceeds its limit.
- Documentation: The software documentation should list all tasks with interval, priority, assigned programs and watchdog settings. Response time calculations need this information. Changing a task interval changes the timing of every program assigned to it.
Task vs. DITA task
In PLC programming, a task schedules code execution. In technical writing, a DITA task is a topic type for step-by-step procedures. The two share only the word.