IEC step

Along with the simplified steps the standard IEC steps in SFC are available.

In order to be able to use IEC steps, you must link the special SFC library lecsfc.lib into your project.

Not more than nine Action can be assigned to an IEC step. IEC actions are not fixed as input, step or output actions to a certain step as in the simplified steps, but are stored separately from the steps and can be reused many times within a POU. For this they must be associated to the single steps with the command ‘Extras”Associate action’.

Along with actions, Boolean variables can be assigned to steps.

The activation and deactivation of actions and boolean variables can be controlled using so-called Qualifier. Time delays are possible. Since an action can still be active, if the next step has been processed, for example through the qualifier S (Set), one can achieve concurrent processes.

An associated boolean variable is set or reset with each call of the SFC block. That means, that at each call the variable gets re-assigned value TRUE resp. FALSE.

The actions associated with an IEC step are shown at the right of the step in a two-part box. The left field contains the qualifier, possibly with time constant, and the right field contains the action name respectively boolean variable name.

An example for an IEC step with two actions:

In order to make it easier to follow the processes, all active actions in online mode are shown in blue like the active steps. After each cycle a check is made to see which actions are active.

Pay attention here also to the restrictions on the use of time-qualifiers in actions that are repeatedly re-used within the same cycle.

Note

If an action has been inactivated, it will be executed once more. That means, that each action is executed at least twice (also an action with qualifier P).

In case of a call first the deactivated actions, then the active actions are executed, in alphabetical order each time.

Whether a newly inserted step is an IEC step depends upon whether the menu command ‘Extras’ ‘Use IEC-Steps’ has been chosen.

In the Object Organizer the actions hang directly underneath their respective SFC POUs. New actions can be created with ‘Project’ ‘Add Action’.

In order to use IEC steps you must include in your project the special SFC library Iecsfc.lib .