Glossary · Automation software engineering and architecture
Event-triggered execution
Also known as: Event-driven execution
German: Ereignisgesteuerte Ausführung
In real-time and automation software, event-triggered execution is an execution model in which a task or function runs in response to the occurrence of an event, such as an interrupt, a signal change or a received message, rather than at fixed time intervals.
- Software engineering
In one sentence
Event-triggered execution runs a task when an event occurs, such as an interrupt or message, rather than at fixed time intervals.
Example
A registration mark sensor triggers an event task in the PLC that captures the axis position immediately, independent of the 10 ms cyclic task.
How it applies
- Engineering: Event-triggered execution gives fast responses to sporadic events and saves processing time when nothing happens. PLC runtimes offer event or interrupt tasks alongside cyclic tasks; IEC 61499 function blocks execute on events by design.
- Timing: The load depends on the event rate, which is not always under control. Bursts of events, such as a chattering sensor, can overload the system unless events are filtered, rate-limited or buffered.
- Documentation: Document which events trigger which tasks, their expected rates, priorities and the maximum tolerable event frequency. Service documentation should explain symptoms of event overload.
Event-triggered vs. time-triggered execution
In time-triggered or cyclic execution, tasks run at fixed intervals regardless of events, as in the classic PLC scan cycle. Time-triggered systems are easier to analyze for worst-case timing; event-triggered systems react faster to rare events. Many controllers combine both models.