Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Communication
208
Function Manual, 05/2021, A5E03735815-AJ
9.3.2 Configuring access to PLC tags
9.3.2.1 Managing write and read rights
Enabling PLC tags and DB tags for OPC UA
OPC UA clients can have read and write access to PLC tags and DB tags if the tags are enabled
for OPC UA (default setting). For an enabled tag the check box "Accessible from HMI/OPC UA"
is activated.
You can change the default setting in the settings of the TIA Portal: Command "Settings > PLC
programming > General" in "Options" menu. You will find the corresponding options in the
"Block interface/data block elements" area.
The following example shows an array data block:
Figure 9-10 Enabling PLC tags and DB tags for OPC UA tags
This array can be read completely in one pass by OPC UA clients (see Addressing nodes
(Page 161)). The check boxes at "Accessible from HMI/OPC UA" and "Writable from HMI/OPC
UA" are activated for all the components of the array.
Result: OPC UA clients can both read and write these components.
Removing write rights
If you want to write-protect a tag, deselect the "Writable from HMI/OPC UA" option for that
tag. This removes the write right for the OPC UA clients and HMI devices.
Result: Only read access by OPC UA clients and HMI devices is possible. OPC UA clients cannot
assign values to this tag and therefore cannot influence execution of the S7 program.
Removing write and read rights
To write-protect and read-protect a tag, disable the "Accessible from HMI/OPC UA" option for
that tag (checkbox not selected). This makes the OPC UA server remove the tag from its
address space. OPC UA clients can no longer see that CPU tag.
Result: OPC UA clients and HMI devices can neither read nor write the tag.