Siemens SIMATIC ET 200AL - Page 902

OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Communication
216 Function Manual, 12/2017, A5E03735815-AF
Example of the assignment of write and read rights (read+write)
Definition of write and read rights in STEP 7
When you define tags, you specify the access rights using the properties "Accessible from
HMI/OPC UA" and "Writable from HMI/OPC UA".
Example of the assignment of write and read rights
Interaction between write and read rights
If you have imported an OPC UA server interface and AccessLevel attributes are set in this
OPC UA XML file, the write and read rights are defined by the following rule: The least
extensive access rights for each setting apply.
Example
● AccessLevel = 1 (read only) in the OPC UA server interface
● Both "Accessible from HMI/OPC UA" and "Writable from HMI/OPC UA" are selected in
the PLC tag table
Result: The tag is only read.
Rules
If write rights are required:
● AccessLevel = 2 oder 3
● "Writable from HMI/OPC UA" enabled
If read rights are required:
● AccessLevel = 1 (AccessLevel 3 is also possible, but misleading. The settings suggests
that an OPC UA client has write and read rights)
● "Accessible from HMI/OPC UA" enabled, "Writable from HMI/OPC UA" disabled
If neither read nor write rights are to be granted (no access):
● AccessLevel = 0
● "Accessible from HMI/OPC UA" disabled
Only one of the two conditions needs to be met to block all access. In this case, review
whether the tag in the OPC UA server interface is actually necessary at all.