Rules For The User Program - Siemens SIMATIC ET 200AL System Manual

OPC UA communication
9.5 Tips and recommendations
9.5.2

Rules for the user program

User programs for OPC UA
The following rules apply to user programs:
• If your application allows it and the communication load is high, you should set a
minimum time for cycle OBs.
Advantages:
– The cycle time remains constant for the most part
– The CPU has more time for communication tasks throughout
Tip: Use the instruction "Runtime_Info"; mode 21 or mode 25 (see TIA Portal Help) to
analyze the CPU utilization (e.g. communication).
• Reduce the number of variables or data blocks that can be reached from OPC UA/HMI. By
default, all variables from OPC UA/HMI are accessible when creating variables/DBs/IDBs.
This measure leads to improved performance when loading in RUN.
Tip: Using the detailed object display in the TIA Portal, you can easily mark the non-OPC-
UA-relevant data blocks as "not accessible from OPC UA".
• Consistent transfer of data beyond the limits of simple data types is only possible with OPC
UA methods. If you use other OPC UA functions (Subscriptions, Read/Write), you must
ensure data consistency in the application.
• OPC UA offers the "RegisterNodes" service for repeated read and write accesses to the
same variables. Servers can use this service to prepare for optimized access to variables.
The instruction "OPC_UA_NodeGetHandleList" of the S7-1500 as OPC UA client implicitly
calls this service to prepare the server for optimized accesses (in OPC UA usage "Registered
Read/Write").
Calling detailed object display in the TIA Portal
To call up the detailed object display, proceed as follows:
1. Switch to the "PLC Programming" portal in the portal view.
2. Select "Show all objects".
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Function Manual, 05/2021, A5E03735815-AJ
Communication