12 Communications Performance and Communications Load
12-22
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
This section describes the data processing time required to transfer data between the EtherNet/IP Unit
and the CPU Unit.
The time required for data processing consists of the following four elements.
1. Variable Access Time
First, we calculate the time required to transfer tag data.
This calculation is performed for each task. Therefore, if multiple tag sets are set for the same
refreshing task, use the total for all tag values in the tag sets.
2. Number of Data Transfers
Tag data is transferred as a part of the task processing.
Therefore, if the time required to process the data transfer is greater than the time allowed for data
transfer in the task process (i.e., the variable access time), the data cannot be sent entirely during
one task period and is sent in fragments instead.
Number of data transfers = (Time required for data transfer
*1
÷ Variable access time set for the
task
*2
) + 1
*3
*1 This is the time required for data transfer as calculated in (1) above.
*2 This is the variable access time that is set for each task in the Task Setup.
*3 Delay in Data Transfer between the CPU Unit and an EtherNet/IP Unit
Precautions for Correct UsePrecautions for Correct Use
The maximum number of words that can be transferred through the EtherNet/IP Unit is 9,600
words for tag data links. 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 in multiple
data exchanges.
12-3-2 EtherNet/IP Unit Data Processing Time
Data Processing Time Overview
CPU Unit model Refreshing direction Formula
NJ501-@@@@ CPU Unit to EtherNet/IP Unit (Number of variables × 3.18 μs) + (Total number of
bytes in variables × 0.0086 μs) + 1 μs + 6.68 μs
EtherNet/IP Unit to CPU Unit (Number of variables × 1.58 μs) + (Total number of
bytes in variables × 0.0051 μs) + 1 μs + 6.68 μs
NJ301-@@@@ CPU Unit to EtherNet/IP Unit (Number of variables × 4.08 μs) + (Total number of
bytes in variables × 0.01 μs) + 1 μs + 7.52 μs
EtherNet/IP Unit to CPU Unit (Number of variables × 2.14 μs) + (Total number of
bytes in variables × 0.0078 μs) + 1 μs + 7.52 μs
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