Principle

In Structured Text, a user function block is called by a DFB call: name of the DFB instance followed by a list of arguments. Arguments are displayed in the list between brackets and separated by commas.

The DFB call can be of one of two types:

• a formal call, when arguments are assignments (parameter = value). In this case, the order in which the arguments are entered in the list is not important.

  The EN input parameter and the ENO output parameter can be used to control the execution of the function block

• an informal call, when arguments are values (expression, object or an immediate value). In this case, the order in which the arguments are entered in the list must follow the order of the DFB input parameters, including for non-assigned inputs (the argument is an empty field)

  It is not possible to use EN and ENO parameters.

DFB_Name (argument 1,argument 2,....,argument n)

Use of EN\ENO Parameters

See EN and ENO Parameters

Example of a DFB

The following simple example explains the different DFB calls in Structured Text language. This is the instance Cpt_1 of the Cpt_parts: type DFB.

Formal DFB Call

The formal DFB call Cpt_1 is performed with the following syntax:

Cpt_1 (Reset:=Clear, Presel:=P_Select, Count:=100, Done=>%Q1.2.1);

Where the input parameters assigned by a value (expression, object or immediate value) are entered in the list of arguments, the syntax is:

Cpt_1 (Reset:=Clear, Presel:=P_Select, Count:=100);

...

%Q1.2.1:=Cpt_1.Done;

Elements of the Sequence

The following table lists the different elements of the program sequence, when a formal DFB call is made.

Informal DFB Call

The informal DFB call Cpt_1 is performed with the following syntax:

Cpt_1 (Clear, %MD10, , 100);

...

%Q1.2.1:=Cpt_1.Done;

Elements of the Sequence

The following table lists the different elements of the program sequence, when a formal DFB call is made.