Omron CJ1W-EIP21 Operation Manuals page 145

Additional Information
If a program needs to access a network variable with an AT specification, set the program in the
primary periodic task so that it matches the refresh timing of the network variable that uses an
AT specification.
Additional Information
Relationship between Refreshing Tasks and Data Concurrency in Tag Data Links
If you do not specify a refreshing task for global variables in tag data links, the following may
occur.
1. When the data is sent for the output tag set, another task may have already written different
values before that data is sent, depending on the timing of the task.
2. When data is received by an input tag set, another task may write different values after that
data is received, depending on the timing of the task.
Therefore, to maintain the concurrency of data in tag data links, you must specify the same
refreshing task on both the output CPU Unit and the input CPU Unit.
This variable may
already be written
by another task
before you send
the data.
 Required Processing Time to Maintain Concurrency
When you set a refreshing task for tags (network variables) to maintain the concurrency of data link
data, the processing time required for that specified task increases. Due to this increase in task pro-
cessing time, the refreshing of tag data link data may not occur during the packet interval (RPI)
period set for each connection. Therefore, you need to adjust the packet interval (RPI) settings to
match the period of the task specified as the refreshing task. Refer to 12-3-3 Effect of Tag Data
Links on Task Periods for details.
 Task Setup Procedure
(1) Set the global variables for which to specify a refreshing task, and set the refreshing
tasks and accessing tasks in the Settings for Exclusive Control of Variables in Tasks
in the Task Setup on the Sysmac Studio.
(2) Set the variable access time for each refreshing task.
For details, refer to the NJ-series CPU Unit Software User's Manual (Cat. No. W501).
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
NJ-series CPU Unit
Refreshing
task
Tag set
Connection
Variable a
Variable b
Tag data links
updated.
Variable c
EtherNet/IP
7 Tag Data Link Functions
NJ-series CPU Unit
Refreshing
task
Tag set
This variable
may be written
Variable d
by another task
after you receive
Variable e
the data.
Variable f
Data concurrency is not maintained
unless you assign the same
refreshing task for both the output
and the input tags.
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