Object 'Interface Property'

Symbol: _cds_icon_interface_property

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.

See also

Example

Declaration and implementation of the interface property ‎Literal_A‎

This 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 when the application is in runtime mode: