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 with the A
T
specification. (This applies to NX102, NX1P2 and NJ-series CPU Units.)
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 data is sent for the output tag set, another task may have already written different val-
ues 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 concurrency of data in tag data links, you must specify the same re-
freshing task on both the output CPU Unit and the input CPU Unit.
NJ/NX-series CPU Unit
Connection
Tag data links
updated.
NJ/NX-series CPU Unit
Refreshing
task
Refreshing
task
EtherNet/IP
Variable c
Variable b
Variable a
Tag set
Variable f
Variable e
Variable d
Tag set
This variable may
already be written
by another task
before you send
the data.
This variable
may be written
by another task
after you receive
the data.
Data concurrency is not maintained
unless you assign the same
refreshing task for both the output
and the input tags.
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 proc-
essing time, tag data link data may not be refreshed at 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 speci-
fied as the refreshing task.
Refer to 15-3-3 Relationship between T
ask Periods and Packet Intervals (RPIs) on page 15-25 for de-
tails.
7 Tag Data Link Functions
7-17
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
7-1 Introduction to Tag Data Links
7
7-1-7 Concurrency of Tag Data Link Data
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