To find out why your driver is transmitting
but not receiving messages:
- Make sure the items have valid item IDs and access paths.
- If you are using asynchronous I/O, the driver may be issuing read requests that are not being acknowledged by the OPC server. Look at the Debug2 messages in the driver’s Server window to determine if the OPC server is receiving bad asynchronous callbacks.
- An exception occurred while the driver was performing a read request to the OPC server.
- If you are connected to an OPC server on a remote computer and are using asynchronous I/O, you may have a security problem. The remote server may not have rights to access your local node. Verify that the server can authenticate your account on the local node. Also ensure that your local node can authenticate the account on the server. Refer to I cannot connect to a remote server for additional DCOM security information.
At this point, we strongly recommend reducing the configuration to one server, one group, and one item. This makes it easier to focus on the problem.
To reduce the configuration
to one server, one group, and one item:
- Disable all but one server.
- On the enabled server, disable all but one group.
- On the enabled group, disable all but one item.
- At the group level, try both synchronous and asynchronous communications. If synchronous communications lets you receive the correct data, but asynchronous does not, you have a security problem. Refer to I cannot connect to a remote server for additional information on DCOM (Distributed Component Object Model) security.
- At the item level, verify that the item ID and access path are both correct, and the requested data type is valid for the selected item ID.
See Also
