Object: Interface Property

Symbol:

Interface properties are an extension of the IEC 61131-3 standard and a tool for object-oriented programming. An interface property declares the accessor methods Get and Set (no implementation code). Therefore, a function block that implements an interface also inherits their interface properties.

You can add an interface property to the device tree for an interface. Then an interface is extended with the accessor methods Get and Set. The Get accessor is for read access. The Set accessor is for write access. You can delete an unneeded accessor. Click Project → Add Object → Interface Property . to add an accessor. The Add Interface Property dialog opens.

Example

Example 526. Declaration and implementation of the interface property Literal_A

The interface itf_A has the property Literal_A with the accessor methods Get and Set.

The function blocks fb_A1 and fb_A2 implement the interface itf_A and therefore inherit its interface property. Each FB has its own implementation.

Interface itf_A

INTERFACE itf_A
VAR
END_VAR
PROPERTY Literal_A : STRING

FB fb_A1

FUNCTION_BLOCK fb_A1 IMPLEMENTS itf_A
VAR
        str_1 : STRING;
        str_2 : STRING;
        iCnt : INT;
END_VAR
iCnt := iCnt + 1;

str_1 := 'Function block A1';

Accessor fb_A1.Literal_A.Get

VAR
END_VAR
Literal_A := CONCAT (str_1,' and property.');

Accessor fb_A1.Literal_A.Set

VAR
END_VAR
str_2 := Literal_A;

FB fb_A2

FUNCTION_BLOCK fb_A2 IMPLEMENTS itf_A
VAR
        str_1 : STRING;
        str_2 : STRING;
        iCnt : INT;
END_VAR

iCnt := iCnt + 1;
str_1 := 'Function block A2';

Accessor fb_A2.Literal_A.Get

VAR
END_VAR
Literal_A := str_1;

Accessor fb_A2.Literal_A.Set

VAR
END_VAR
str_2 := Literal_A;

Program PLC_PRG

PROGRAM PLC_PRG
VAR
        iCnt : INT;
        my_1 : fb_A1;
        my_2 : fb_A2;
        strName_1 : STRING;
        strName_2: STRING;
END_VAR

iCnt := iCnt + 1;
my_1();
my_2();
strName_1:= my_1.Literal_A;
strName_2:= my_2.Literal_A;
my_1.Literal_A := 'Hello 1';
my_2.Literal_A := 'World 2';

This leads to the following monitoring of PLC_PRG at application runtime: