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CIP Services and User-created Tags
Chapter 2
Rockwell Automation Publication 1756-PM020F-EN-P - January 2019
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The amount of data returned (0x20 bytes) agrees with the value of Attribute 5
(Template Structure Size = 0x20 as determined in Step 3) using the
Get_Attributes_List service.
See also
Step 4: Determining the data packing of the members of a structure
CIP Services and User-created Tags
The client application should periodically check for changes in the controller
to determine if it must repeat the process outlined in this chapter. Once
controller program development is complete, tags and UDT definitions
generally remain constant; however, it is possible that a PLC program
developer may create or delete tags from time to time, or change a UDT
definition. When that happens, the symbol object instance associated with a
tag may change, the relationship between the template instance and the
symbol instance may change, or the data makeup of a UDT-based tag can
change.
See also
Controller object attributes indicate changes made to the controller. A
change in these values indicates changes to symbol instances, template
instances, or both. These are not the only changes indicated by these
attributes, but these provide the most straightforward way to determine when
the client application should refresh the list of created tags, while keeping the
number of false indications to a minimum.
For client applications, use the Get_Attribute_List service to periodically
retrieve attributes 1, 2, 3, 4 and 10 of class 0xAC in the controller. If the
value of these attributes changes between reads, the client application must
refresh the:
•
List of symbols
•
Association between symbols and templates
•
Template information.
To verify these attributes, use the Multi Service Packet Service (0x0a) to
group the Get_Attribute_List service with the Read Tag services. If the
situations occur, discard the Tag Read reply data and refresh the symbol and
template information:
•
The values returned for these attributes are different than the last time
they were read.
Step 5: Determine when the
tags list and structure
information need
refreshing
How to detect changes