13-23
13 Communications Performance and Communications Load
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
13-3 I/O Response Time in Tag Data Links
13
13-3-3 Relationship between Task Periods and Packet Intervals (RPIs)
Time required for the data transfer: 11.92 µs + 9.44 µs+13.3 µs = 34.66 µs
Variable access time set for the task: 500 µs × 0.03 = 15 µs
Number of data transfers: 34.66 µs ÷ 15 µs = 2.31 times
Thus, approximately three data transfers are required.
3
Calculate the actual time required for the data transfer.
500 µs × 3 times = 1,500 µs
The tag data is transferred during task processing. Therefore, the tag data transfer process is added to
the task processing for tasks set as a tag’s refreshing task. This requires you to make adjustments to
the variable access time and task period in the Task Setup so that these processes are completed
within a single task period.
1
The time required for the data transfer is calculated using the following formula and is set as the
variable access time
*1
.
(Number of variables × 0.55 µs) + (Total number of bytes in variables × 0.0007 µs) + 7.1 µs
* 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).
Tag data is transferred based on the actual time required for the transfer (task period × number of data
transfers), regardless of the packet interval (RPI) setting. Therefore, set the packet interval (RPI)
according to the following guideline.
Actual time required for data transfer (Task period × Number of data transfers) < RPI
For details on the actual time required to transfer data, refer to
13-3-2 Built-in EtherNet/IP Port Data
Processing Time
.
Example: Relationship between the RPI Setting and the Time Required for Data Transfer
• Task period: 10 ms
• Number of data transfers: 2
• Actual time required for data transfer: 10 ms × 2 times = 20 ms
Regardless of the RPI value, the time required for the data transfer is 20 ms.
13-3-3 Relationship between Task Periods and Packet Intervals (RPIs)
Effect of Tag Data Links on Task Periods
Adjusting Packet Intervals (RPIs) According to the Task Periods
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