Precautions for Correct Use
The maximum number of tag data link words that can be transferred through a built-in
EtherNet/IP port is 184,832 words on an NX701 CPU Unit (total of 369,664 words with the two
ports), 9,600 words on an NX102 CPU Unit (total of 19,200 words with the two ports), and
9,600 words on an NX1P2 CPU Unit or NJ-series CPU Unit.
If the number of tag data link words exceeds the number of words that can be exchanged with
the CPU Unit at one time, the data is divided and transferred over multiple times
3. Actual Time Required for Data Transfer
Y
ou 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
Data Processing Time Calculation Example
The following shows an example to explain how to calculate the time required for tag data transfer.
•
CPU Unit model
NJ501-££££
• Refreshing task
Primary periodic task
Task period: 500μs (variable access time: 3%)
• Settings of tag sets
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
1 Calculate the variable access time as shown below.
[(600 + 200 + 1,000) bytes × 0.001 μ
s] + [(8 + 4 + 10) variables × 0.49 μs] + 3 × 1.41 μs + 6.68
μs = 23.49 μs
2 Calculate the number of data transfers.
Time required for data transfer: Variable access time in step1 = 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 entire data transfer.
500 μs × 2 times = 1,000 μs
15 Communications Performance and Communications Load
15-24
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
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