14 Communications Performance and Communications Load
14-24
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
3. Actual Time Required for Data Transfer
You can use the task period of the refreshing task and the number of data transfers as calculated in
(2) above to calculate the actual time required to transfer the data.
Task period × Number of data transfers
Here we provide an example of how to perform the tag data link calculations described earlier for the
following tag data transfers.
• Model Numbers of CPU Units for Tag Data Links
NJ501-
• 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.
[(600 + 200 + 1,000) bytes × 0.001 μs] + [(8 + 4 + 10) variables × 0.49 μs] + 3 × 1.41 μs
+6.68μs = 23.49 μs
2
Calculate the number of data transfers.
Time required for data transfer: “Variable access time” in step 1 = 23.49 μs
Variable access time set for the task: 500 μs × 0.03 = 15 μs
Number of data transfers: 23.49 μs ÷ 15 μs = 1.6 times
Thus, approximately two data transfers are required.
3
Calculate the actual time required for the data transfer.
500 μs × 2 times = 1,000 μs
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
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