OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Communication
Function Manual, 11/2019, A5E03735815-AH
171
9.3.2.4 Consistency of CPU tags
"AccessLevelEx" attribute extends access properties
As of firmware version V2.6, the OPC UA server of the S7-1500 CPU supports not only the
attribute "AccessLevel" (see Coordinating write and read rights for CPU tags (Page 169)) but
also the attribute "AccessLevelEx" which, in addition to the already explained bits for read
access and write access, provides information on the consistency of a OPC UA tag. The new
attribute was introduced with version V1.04 of the OPC UA specification (Part 3, Address
Space Model).
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).
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