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
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Function Manual, 05/2021, A5E03735815-AJ
Reading consistency properties
In the OPC UA information model of the OPC UA server, the attribute "AccessLevel" defines
the access.
AccessLevelEx is defined bit by bit; in this case the relevant bits are:
•
Bit 0 = CurrentRead
• Bit 1 = CurrentWrite
• Bits 2 to 7 are not relevant for the OPC UA server of an S7-1500 CPU
The meaning of the bit combinations is explained in the section on read and write rights.
The following bits for consistency are also added:
•
Bit 8 = NonatomicRead; the bit is set if the tag cannot be read consistently. For read
consistency of tags, bit 8=0.
• Bit 9 = NonatomicWrite; is set if the tag cannot be written consistently. For write
consistency of tags, or if no write access is granted, bit 9=0.
Examples
An OPC UA tag (structure) is readable and writable; but inconsistent for reading and writing
access.
Consequently: Bits 0, 1, 8 and 9 are set: AccessLevelEx = "771" (1+2+256+512).
Another structure is read-only.
Consequently: Bits 0 and 8 are set, bit 1 and bit 9 are not set: AccessLevelEx = "257"
(1+0+256+0).
Handling of the attribute in the server
The "AccessLevelEx" attribute is only available in the OPC UA server. The attribute is not
present in a node set file (XML export file).
However, the attribute "AccessLevel", which is exported, includes the information from
"AccessLevelEx", see next section.
Export
During XML export of the standard SIMATIC server interface, the server sets the "AccessLevel"
attribute, which was expanded to 32 bits in V1.04 compared to V1.03, to the value of the
"AccessLevelEx" attribute.
Import
When importing a node set file (e.g. from an export of a server interface), the S7-1500 CPU
sets the attribute "AccessLevelEx" according to its own estimate of the consistency of the
imported data type, see next section. The imported value is ignored.