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.16.

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.66:

Table A.66 – OPC UA Read error mapping

OPC UA Status Code	OPC DA Error ID
Bad_OutOfMemory	E_OUTOFMEMORY
Bad_NodeIdInvalid	E_INVALIDITEMID
Bad_NodeIdUnknown	E_UNKNOWNITEMID
Bad_NotReadable	E_BADRIGHTS
Bad_UserAccessDenied	E_ACCESSDENIED
Bad_AttributeIdInvalid	E_INVALIDITEMID
Bad_UnexpectedError	E_FAIL
Bad_InternalError	E_FAIL
Bad_SessionClosed	E_FAIL
Bad_TypeMismatch	E_BADTYPE