The IEC 61131-3 key word mapping to OPC UA Properties is 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 Property RETAIN 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 Blocks and Ctrl Programs).
The Property NON_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 Blocks and Ctrl Programs).
The Property CONSTANT 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 Variable cannot be modified.
The Property AT contains the location assignment to the Ctrl Variable as string if the AT key word is set for the Ctrl Variable.
The IEC standard does not define key words to configure information like the value range or the engineering unit for a Ctrl Variable. The configuration in a programming system is vendor specific but this specification defines the export format in the PLCopen XML Additional Data in the XML element addData.
The InstrumentRange Property defined in OPC 10000-8 shall be provided in the XML element UaInstrumentRange as part of the XML element representing the Ctrl Variable. The attributes of the XML element are formally defined in Table 35.
Table 35 – Range XML attributes
|
Name |
Type |
Use |
Default |
|
|
Low |
double |
required |
|
|
|
High |
double |
required |
|
|
The EURange Property defined in OPC 10000-8 shall be provided in the XML element UaEURange as part of the XML element representing the Ctrl Variable. The attributes of the XML element are formally defined in Table 35.
The EngineeringUnits Property defined in OPC 10000-8 shall be provided in the XML element UaEngineeringUnits as part of the XML element representing the Ctrl Variable.