What You Need To Know About Opc Ua Clients - Siemens SIMATIC ET 200AL System Manual

OPC UA communication
9.1 What you need to know about OPC UA
9.1.10

What you need to know about OPC UA clients

Basics of OPC UA clients
OPC UA clients are programs that do the following:
● Read and write information from an OPC UA server, for example an S7-1500 CPU
● Execute methods through the OPC UA server
However, OPC US clients can access data that is enabled for this purpose (see "Managing
write and read rights (Page 157)").
You need the endpoint of the server to establish a connection to an OPC UA server (see
"Endpoints of the OPC UA servers (Page 138)").
Reading out information from the OPC UA server
When a connection to an end point of the server exists, you can use the navigation function
of the client: You navigate starting from a defined starting point (from the "root" node)
through the address space of the server.
The following information is provided in the process:
● Enabled PLC tags, data blocks and data block components
● Namespace index and identifiers of these PLC tags, data blocks and DB components
● Data types of the PLC tags and DB components
● Number of components in arrays (required for reading and writing arrays)
In addition, you receive information about the OPC UA server itself as well as information
about the S7-1500 based on the "OPC UA for Devices" standard of the OPC Foundation (for
example, serial number, firmware version).
Reading data from the server and writing to the server
You now know the namespace, identifier and data type of PLC tags. This means that you
can now specifically read individual PLC tags and DB components as well as complete
arrays and structures. Examples for reading Boolean tags and array data blocks are
available under Addressing nodes (Page 132).
With the information that you obtain while navigating through the address space of the server
(index, identifier and data type), you can also transfer values to the S7-1500 with the OPC
UA client. The following example overwrites the first three values in the array data block
"MyDB".
For "Array Range" you specify which components of the array you want to overwrite. The
"Good" status code indicates that the values were transferred successfully. However, you
can only write the values to the S7-1500 but not the time stamps of these values. The time
stamps can only be read.
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Communication