14-25
14 Communications Performance and Communications Load
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
14-3 I/O Response Time in Tag Data Links
14
14-3-3 Relationship between Task Periods and Packet Intervals (RPIs)
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
Calculate the time required for the data transfer and set the result as the "variable access
time"
*
.
For the formula for calculating the time required for the data transfer, refer to Data Processing
Time Calculation Example.
* If the same refreshing task is set for multiple tag sets, calculate the total time required for all tags in tag
sets.
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/NX-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 14-3-2 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.
14-3-3 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
Task period: 10 ms
Example: Primary periodic task
To Controller #2
To Controller #2
Refreshing period
during RPI
10 ms
I/O refreshing
User program execution
Motion control
Send data
processing
Send data
processing
Task period × 2
Time required to transfer data from Controller #1: 20 ms
Task period: 10 ms
Example: Primary periodic task
RPI of 10 ms
RPI of 20 ms
Task period × 2
(1)
(2)
(1) (2)
Refreshing period
during RPI:
20 ms
Transmission
path
Transmission
path
Controller#1
Controller#1
Data link processing
(system common processing 3)
OI MC
UPG
OI
UPG
MC
Tag data link service
Tag data link service
OI MC
UPG
OI MC
UPG
OI MC
UPG
OI MC
UPG
OI MC
UPG
OI MC
UPG
OI MC
UPG
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