Object 'Property'

Symbol: _cds_icon_interface_property

Keyword: ‎PROPERTY‎

Properties are an extension of the IEC 61131-3 standard and a tool for object-oriented programming.

Properties are used for data encapsulation because they allow for external access to data and act as filters at the same time. For this purpose, a property provides the accessor methods ‎Get‎ and ‎Set‎ which allows for read and write access to the data of the instance below the property.

You can add a property with accessor methods below a program, a function block, or a global variable list. Click “Project Add Object Property” to open the “Add Property” dialog.

You can add an interface property below an interface.

When you copy a property that is inserted below a POU and add it below an interface, or if you move the property there, the included implementations are removed automatically.

See also

⮫ “Object 'Interface Property'”

Dialog 'Add Property'

Function: Creates a new property below the selected POU when the dialog is closed.

Call: Menu bar: “Project Add Object Property”; context menu

Requirement: A program (‎PRG‎), a function block (‎FUNCTION_BLOCK‎), or a global variable list (‎GVL‎) is selected in the “POUs” view or the “Devices” view.

“Name”	Name (identifier) of the property Example: `‎prop_iA‎`
“Return type”	Default type or structured type of return value Example: `‎INT‎`
“Implementation language”	Example: “Structured Text (ST)”

“Access specifier”	Controls access to data
“PUBLIC” or unspecified	Access is not restricted.
“PRIVATE”	Access is restricted to the program, function block, or GVL. The object is marked as `‎(private)‎` in the POU or device view. The declaration contains the keyword `‎PRIVATE‎`.
“PROTECTED”	Access is restricted to the program, function block, or GVL with its derivations. The object is marked as `‎(protected)‎` in the POU or device view. The declaration contains the keyword `‎PROTECTED‎`.
“INTERNAL”	Access is restricted to the namespace (library). The object is marked as `‎(internal)‎` in the POU or device view. The declaration contains the keyword `‎INTERNAL‎`.

“Abstract”	: Identifies that the property does not have an implementation and the implementation is provided by the derived FB
“Add”	Adds a new property be low the selected object and below that the accessor methods `‎Get‎` and `‎Set‎` Note: When you select a property, you can also add a previously removed accessor explicitly by clicking “Add Object”.

Editor 'Property'

You can program the data access in the editor. The code can contain additional local variables. However, it must not contain any additional input variables or (as opposed to a function or method) output variables.

Example

Function block FB_A

FUNCTION_BLOCK FB_A
VAR_INPUT
END_VAR
VAR_OUTPUT
END_VAR
VAR
    iA : INT;
END_VAR

iA := iA + 1;

Property ‎prop_iA‎

PROPERTY PUBLIC prop_iA : INT

Accessor method FB_A.prop_iA.Get

prop_iA := iA;

Accessor method FB_A.prop_iA.Set

iA := prop_iA;

PROGRAM PLC_PRG
VAR
	fbA : FB_A;
	iVar: INT;
END_VAR

fbA();
IF fbA.prop_iA > 500 THEN
	fbA.prop_iA := 0;
END_IF
iVar := fbA.prop_iA;

‎Get‎ and ‎Set‎ accessors

The call of the ‎Set‎ accessor is written to the property. Then it is used in the same way as an input parameter. When the Get accessor is called, the property is read. It is used in the same way as an output parameter. Access is restricted in each case by means of access modifiers (qualifiers). As a result, the objects are identified accordingly.

When a property is accessed as read only or write only, you can delete the unneeded accessors.

You can add accessors explicitly by selecting a property and clicking “Add Object”. A dialog opens, either “Add Get accessor” or “Add Set accessor”. There you can set the implementation language and the access.

Table 466: Dialog “Add Get (Set) Accessor”
“Implementation language”	Example: “Structured Text (ST)”

“Access specifier”	Qualifier for the declaration part
`‎PUBLIC‎` or unspecified	Access is not restricted.
`‎PRIVATE‎`	Access is restricted to the program, function block, or GVL. The object is marked as `‎(private)‎` in the POU or device view. The declaration contains the keyword.
`‎PROTECTED‎`	Access to the property is restricted to the program, function block, or GVL and its derivations. The declaration contains the keyword. The object is marked as `‎(protected)‎` in the POU or device view.
`‎INTERNAL‎`	Access to the method is restricted to the namespace (the library). The object is marked as `‎(internal)‎` in the POU or device view. The declaration contains the keyword.

“Add”	Adds the accessor methods `‎Get‎` or `‎Set‎` below the selected property.

Monitoring of properties in online mode

The following pragmas are provided for the monitoring of properties in online mode. You insert them at the top position of the property definition:

‎{attribute 'monitoring' := 'variable'}‎

Each time the property is accessed, CODESYS saves the actual value to a variable and displays the value of this variable. This value can become outdated if no more access to the property takes place in the code.
‎{attribute 'monitoring' := 'call'}‎

Each time the value is displayed, CODESYS calls the code of the ‎Get‎ accessor. If this code contains a side effect, then the monitoring executes the side effect.

You can monitor a property with the help of the following functions.

Inline monitoring

Requirement: The “Enable inline monitoring” option is selected in the “Text Editor” category of the “Options” dialog.
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