Glossary · Distributed automation and IEC 61499
Execution control state
Also known as: EC state
German: Ausführungssteuerungszustand
In IEC 61499, an execution control state (EC state) is a state of a basic function block's execution control chart, with which zero or more EC actions are associated that are executed when the state becomes active.
- IEC 61499
- Standards
In one sentence
An EC state is a state in an IEC 61499 execution control chart; entering it runs its actions, which call algorithms and emit events.
Example
When the EC state REQ becomes active, it runs the algorithm Calculate and emits the event output CNF, then returns to the state IDLE.
How it applies
- Engineering: Each ECC has one initial state, usually called START, and further states for the block's operating conditions. EC actions of a state run once when it is entered; the state then stays active until a transition fires.
- Design: Name states after the condition they represent (IDLE, RUNNING, FAULT) rather than after the algorithm they call. A state without actions can still be useful for waiting.
- Diagnostics: Some runtimes allow the active EC state to be monitored online, which helps to understand why a block does not react as expected.
- Documentation: Describe each state's meaning, its actions and the transitions leaving it. Where a block's state is visible to operators, use the same state names in HMI texts and manuals.
EC state vs. SFC step
An EC state belongs to the state machine of a single basic function block and is evaluated when events arrive. An SFC step belongs to a sequence of an IEC 61131-3 program and is evaluated cyclically. See Sequential function chart (SFC) and the general State transition concept.