Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.1 What you need to know about OPC UA
Communication
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Structures
Structures are transferred as ExtensionObject. The S7-1500 server uses binary representation
for transmission of the ExtensionObjects over the line; the individual structure elements
come one after the other. At the front is the NodeId of the data type; this is used by the client
to establish the structure.
For OPC UA Specification <= V1.03, a client has to read, decode and interpret the complete
DataTypeDictionary for this (unless it has already learned this library offline through an XML
import).
Starting in OPC UA V1.04, the DataTypeDescription attribute is also available for this, which
can be read and interpreted more quickly and easily. A client only determines the setup of the
structure once, before or during the first access, and then uses this information for the
duration of the session.
Special SIMATIC data types
SIMATIC data types that are not in the table above and cannot be defined as elements of a
structure or PLC data type are not supported by the OPC UA client.
These are, for example, "ANY" or "POINTER" pointers, function block "Block_FB", function
"Block_FC" or hardware data type "REMOTE".
The selection of an unsupported data type leads to an error message.
Additional information
More details on mapping of basic data types, arrays and structures can be found in the OPC
UA Specification Part 6, "Mappings" (see OPC UA BINARY there).
What must be considered with arrays and data types DTL and LDT in the OPC UA server of a
SIMATIC S7-1500? FAQ ( https://support.industry.siemens.com/cs/ww/en/view/109766726 )