At a Glance

In addition to the standardized IEC features listed in the IEC Compliance Tables, the Control Expert programming environment inherited a number of features from the PL7 programming environment. These extensions are optionally provided; they can be checked or not in a corresponding options dialog. The dialog and the features are described in detail in a chapter of the online help titled Data and Languages.

Not included in the options dialog is another extension, which is inherited both from the PL7 and the Concept programming environments: Control Expert provides the construct of the so-called Section in all programming languages, which allows to subdivide a Program Organization Unit (POU). This construct introduces the possibility to mix several languages (e.g. FBD sections, SFC sections) in a POU body, a feature which, if used for this purpose, constitutes an extension of the IEC syntax. A compliant POU body should contain a single section only. Sections or Program Units do not create a distinct name scope; the name scope for all language elements is the POU.

Purpose of Sections, or Program Units

Sections, or Program Units serve different purposes:

• Sections, or Program Units allow to subdivide large POU bodies according to functional aspects: the user has the possibility to subdivide his POU body into functionally meaningful parts. The list of sections represents a kind of functional table of contents of a large, otherwise unstructured POU body.

• Sections, or Program Units allow to subdivide large POU bodies according to graphical aspects: the user has the possibility to design substructures of a large POU body according to an intended graphical presentation. He can create small or large graphical sections according to his taste.

• The subdivision of large POU bodies allows quick online changes: in Control Expert, the Section, or the Program Unit serves as the unit for online change. If a POU body is modified during runtime at different locations, automatically all sections affected by the changes are downloaded on explicit request.

• Sections, or Program Units allow to rearrange the execution order of specific, labeled parts of a POU body: the section name serves as a label of that part of the body which is contained inside the section, and by ordering these labels the execution order of those parts is manageable.

• Sections, or Program Units allow to use different languages in parallel in the same POU: this feature is a major extension of the IEC syntax, which allows only one single IEC language to be used for a POU body. In a compliant body, SFC has to be used to manage different languages inside a body (each transition and action may be formulated in its own language).