If in the Entry state the system decides that there is a step sequence to be executed, the SubStateMachine informs the client about this by firing an EnterStepSequence event. It then enters the Wait state to wait for a synchronization event.

The synchronization can occur by a Sync method call from an OPC UA client, typically the control system. The synchronization can also occur internally, typically due to communication events on other interfaces, e.g. a digital trigger.

The system then enters the Step state, where it does the actual work required in this state of the step model and decides whether there are any steps left in the step sequence. This is application-specific, as is the original decision to execute a step sequence at all.

The system indicates the need for another step-sequence cycle by firing a NextStep event and re-enters the Wait state. In this manner, an arbitrary and dynamic number of steps can be executed. It is not necessary to predefine the number of steps.

To use the common example of image acquisition: There may be one image acquisition in each Step state, but it is also possible that the step sequence is used only for mechanical synchronization and all acquisition is done in the Exit state.