OPC UA communication
9.1 What you need to know about OPC UA
Communication
Function Manual, 12/2017, A5E03735815-AF
141
Server response in detail:
● If you request the values of PLC tags, you will get what were the latest values before the
CPU switched to or was set to "STOP".
● If you write values to the OPC UA server, the OPC UA server will accept those values.
However, the CPU will not process the values because the user program is not executed
in "STOP" mode.
An OPC UA client can nonetheless read the new values from the OPC UA server of the
CPU.
● If you call a server method, the error message 16#00AF_0000 (BadInvalidState) is output
because the server method (user program) is not running.
The OPC UA server is stopped upon each download to the CPU (for example after a
configuration or block is downloaded) and then restarts. The restart of the OPC UA server
can take a while depending on the size of the data structure.
Reading CPU operating mode over OPC UA server
The OPC UA server allows you to read out the CPU mode, see figure below:
Figure 9-5 Reading CPU operating mode over OPC UA server
Apart from the operating state of the CPU you can also read out the status (State) of the
server.
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