There are two ways how this OPC UA Mapping can trigger IO-Link ISDU requests:
- Executing some OPC UA Methods (like ReadISDU, WriteISDU, SystemCommand, etc.).
- Reading or writing some OPC UA Variables (which trigger an ISDU request). In both access ways an ISDU request can fail and IO-Link will respond with an ISDU error. In case of error the OPC UA Service response (of Services like Read, Write or Call) should contain information about the error in diagnosticInfos as specified in the following paragraphs. If an ISDU error occurs and the ISDU request was triggered with an OPC UA Method, the output parameter “ErrorType” contains the raw ISDU error as well.
NOTE To get content in the field diagnosticInfos an OPC UA Client has to indicate in the OPC UA Service RequestHeader that diagnostic info associated with the operation of the Service has to be returned. This is done by setting the appropriate bits of returnDiagnostics, a field of the OPC UA Service RequestHeader. (See OPC 10000-4 for more details).