Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.4 Using the S7-1500 CPU as an OPC UA client
Communication
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Function Manual, 05/2021, A5E03735815-AJ
9.4.8 Rules for the access to structures
The rules for the access to structures are explained below. Note these rules when reading and
writing values of complete structures provided by an OPC UA server.
How the client of the S7-1500 CPU accesses structures
The OPC UA client of the S7-1500 CPU uses neither TypeDictionaries nor DataTypeDefinition
attributes, which a server offers for the resolution of these structures.
These options of the OPC UA client for checking structural elements in runtime are limited in
the client.
Rules for the access to structures
If you use the client interfaces to configure the read and write lists (connection
parameterization) and assign the PLC data types to the imported or online determined
address model of the server, the read and write accesses to structures operate trouble-free in
runtime.
The configuration by means of client interface automatically ensures that the sequence and
the data type of the structural elements are coordinated on client and server side.
Recommendation: Update an S7-1500 CPU (as server) to the current firmware version (e.g.
V2.0 > V2.5.2 or higher).
In runtime the OPC UA client only checks the total length of the transmitted value; more
detailed checks are not possible.
Mapping rules apply to the assignment of OPC UA structures to PLC tags or DB tags (see
Mapping of data types (Page 169)). Non-executed data type (such as OPC UA byte strings) are
not supported.
Example of an error-free assignment of the structure elements
In the imported node set file (XML export), the structure is defined as follows: