The IEC 61131-3 key word mapping to OPC UA Propertiesis formally defined in Table 34.

Table 34– IEC 61131-3 Variable Key Word Property Definition

References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Instance of any Variable Type.
HasProperty	Variable	RETAIN	Boolean	PropertyType	Optional
HasProperty	Variable	NON_RETAIN	Boolean	PropertyType	Optional
HasProperty	Variable	CONSTANT	Boolean	PropertyType	Optional
HasProperty	Variable	AT	String	PropertyType	Optional

The PropertyRETAIN indicates if the RETAIN key word is set for the Ctrl Variable. It provides an explicit declaration of “warm start” behaviour of the Ctrl Variable(and Ctrl Function Blocksand Ctrl Programs).

The PropertyNON_RETAIN indicates if the NON_RETAIN key word is set for the Ctrl Variable. It provides an explicit declaration of “warm start” behaviour of the Ctrl Variable(and Ctrl Function Blocksand Ctrl Programs).

The PropertyCONSTANT indicates if the CONSTANT key word is set for the Ctrl Variable. It provides a declaration of a fixed value for the Ctrl Variable. The Ctrl Variablecannot be modified.

The PropertyAT contains the location assignment to the Ctrl Variableas string if the AT key word is set for the Ctrl Variable.