OPC XML Data Access 1.01 Client communication protocol

Protocol specification
Communication line configuration
Protocol configuration on the communication station
I/O tag configuration
Literature
Changes and modifications
Document revisions

Protocol specification

Protocol OPC XML DA is a transitive protokolom between protocols OPC Data Access Client and OPC Unified Architecture Data Access Client.
An improvement to OPC Data Access Client is a transition to platform-independent communication (using XML data format and SOAP-Web Services over HTTP protocol).
The latest from OPC protocol family is the protocol OPC Unified Architecture Data Access Client which maintains platform independence and optimizes performance by replacing XML / SOAP communications with binary encoding and by eliminating HTTP protocol.

Communication line configuration

Communication line category: HTTP client
URL: URL address of OPC XML server in form http://host[:port][/path[?query]], e.g. http://172.16.0.1 or http://myopcserver.domain:8080/opcxml
Proxy: IP address or name of optional proxy server. If entered, KOM process will connect to proxy server instead of host listed in parameter URL.
User: optional name for authentication on proxy server (support for authentication has not been implemented).
Password: optional password for authentication on proxy server (support for authentication has not been implemented).

Protocol line parameters

Parameter	Meaning	Unit	Default value
Debug Responses Parsing	Enable debug messages at the OPC XML server response level.	YES/NO	NO
Debug Http I/O Data	Turn on debug messages at HTTP communication level.	YES/NO	YES
Debug Http Responses	Turn on debug messages with headers and body of HTTP response.	YES/NO	NO
Debug Received Values	Turn on debug messages with received values.	YES/NO	YES

Protocol configuration on the communication station

Communication protocol: OPC XML Data Access 1.01 Client.
Station address: unused.

Station protocol parameters

Table 1

Full name	Description	Default value
Request option ReturnErrorText	Parameter of Subscribe and Write requests. If set to YES, the server will return verbose error description.	NO
Request option ReturnDiagnosticInfo	Parameter of Subscribe and Write requests. If set to YES, the server will return verbose server specific diagnostic information to provide additional information relative to item specific errors.	NO
Request option ReturnItemTime	Parameter of Subscribe and Write requests. If set to YES, the server will return the timestamp for each Item.	YES
Request option ReturnItemPath	Parameter of Subscribe and Write requests. If set to YES, the server will return ItemPath (a path to Item within Namespace) for each Item.	NO
Request option ReturnItemName	Parameter of Subscribe and Write requests. If set to YES, the server will return ItemName (a fully qualified identifier of Item) for each Item.	NO
Request option ReturnValuesOnReply	Parameter of Subscribe and Write requests. If set to YES, the server will return values of all Items in reply to Subscribe and value of Item in reply to Write as if the client had performed a Read request directly after the Write request.	YES

I/O tag configuration

I/O tag configuration dialog window is used for setting the monitored objects.

Object address setting

Name	Meaning
Item Name	Unique text identifier of Data in OPC XML server.
Subscribe	If the setting is checked, the KOM process uses this Item in Subscribe request to query the value of the object. This setting can be unchecked for objects that are not supposed to be read (e.g. write-only I/O tags or objects that have been removed from the communication).