12 Communications Performance and Communications Load
12-24
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
Here we provide an example of how to perform the tag data link calculations described earlier for the
following tag data transfers.
• CPU Unit with Tag Data Links:
NJ501-@@@@
• Connection Direction
The local EtherNet/IP Unit is set as the originator node.
• Refreshing task
Primary periodic task
Task period: 500 μs (variable access time: 3%)
• Setting Tag Sets
1
Calculate the variable access time as shown below.
Tag set A: (8 variables × 3.18 μs) + (600 bytes × 0.0086 μs) + 1 μs + 6.68 μs = 84.72 μs
Tag set B: (4 variables × 3.18 μs) + (200 bytes × 0.0086 μs) + 1 μs + 6.68 μs = 37.6 μs
Tag set C: (10 variables × 3.18 μs) + (1,000 bytes × 0.0086 μs) + 1 μs + 6.68 μs = 125.48 μs
2
Calculate the number of data transfers.
Time required for the data transfer: 8 4.72 μs + 37.6 μs + 125.48 μs = 247.8 μs
Variable access time set for the task:500 μs × 0.03 = 15 μs
Number of data transfers: 247.8 μs ÷ 15 μs = 16.52 times
Thus, approximately 17 data transfers are required.
3
Calculate the I/O refresh processing time.
1 unit × 1 ms + 0.5 ms + 0.5 ms = 2 ms (2,000 μs)
4
Calculate the actual time required for the data transfer.
(500 μs × 17 times + 1 − 1) + 2,000 μs = 10,500 μs
The tag data is transferred during task processing. Therefore, if you need to complete transfer process-
ing for task data within one task period, adjust the variable access time and task period settings in the
Task Setup to change the task period.
1
The time required for the data transfer is calculated for the variable access time. Refer to the fol-
lowing section for the formula to calculate the variable access time. 1. Variable Access Time on
page 12-22
Note If the same refreshing task is set for multiple tag sets, the total of all tag values in the tag sets is used.
2
Set the variable access time in the Task Setup to a value equal to or greater than the value cal-
culated in step 1 above.
Adjust the task period time after adding in the time calculated in step 1. Use the Sysmac Studio
to set the variable access time and task period settings. For details, refer to the NJ-series CPU
Unit Software User’s Manual (Cat. No. W501).
Data Processing Time Calculation Example
Tag set Refreshing task Number of variables Total size of variables
Tag set A Primary periodic task 8 600 bytes
Tag set B Primary periodic task 4 200 bytes
Tag set C Primary periodic task 10 1,000 bytes
12-3-3 Effect of Tag Data Links on Task Periods
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