A.4.4 Read data

The COM UA Proxy converts all the ItemIds in the Read into valid NodeIds by replacing the ‘-’ with ‘=’ and calls the OPC UA Read Service for the Value Attribute.

If the Read Service call is successful then DataValue for each node is mapped to the VQT for each item as shown in Figure A.17.

If the Read Service call fails or If there are errors for some of the Nodes, then the StatusCodes of these Nodes are mapped to the error code by the COM UA Proxy.

The mapping of the OPC UA Status code to OPC DA Read Error code (in the COM UA Proxy) is shown in Table A.8:

Table A.8 – OPC UA Read error mapping
OPC UA Status Code OPC DA Error ID
Bad_OutOfMemoryE_OUTOFMEMORY
Bad_NodeIdInvalidE_INVALIDITEMID
Bad_NodeIdUnknownE_UNKNOWNITEMID
Bad_NotReadableE_BADRIGHTS
Bad_UserAccessDenied E_ACCESSDENIED
Bad_AttributeIdInvalidE_INVALIDITEMID
Bad_UnexpectedErrorE_FAIL
Bad_InternalErrorE_FAIL
Bad_SessionClosedE_FAIL
Bad_TypeMismatchE_BADTYPE