12 Communications Performance
12 - 2
NX-series EtherCAT Coupler Unit User’s Manual (W519)
12-1 Performance of Process Data Com-
munications
This section describes the performance of process data communications when an EtherCAT Slave Ter-
minal is connected to the built-in EtherCAT port on an NJ-series CPU Unit.
The performance of process data communications is different for synchronous I/O refreshing and
Free-Run refreshing.
This section describes the I/O response time for I/O refreshing when the NX Unit operates with syn-
chronous I/O refreshing and the EtherCAT Slave Terminal operates in DC Mode. The I/O response time
is the time required for the following processing: The CPU Unit processes an external signal input to
one NX Unit, and another NX Unit outputs the processed result as an external signal.
When synchronous I/O refreshing is used for more than one EtherCAT Slave Terminal on the same
EtherCAT network, the reading of inputs and the updating of outputs are processed at the same time for
all NX Units that are operating with synchronous I/O refreshing on all of the EtherCAT Slave Terminals.
Therefore, when you calculate the I/O response times for an NX Unit on an EtherCAT Slave Terminal,
you must use in the calculations the longest elements for all of the EtherCAT Slave Terminals. Refer to
10-3-4 I/O Refreshing Method Operation on page 10-7 for details on the operation of synchronous I/O
refreshing.
The calculations that are described in this section assume that the following conditions are met.
(a) Sequence control and motion control in the NJ-series CPU Unit are performed within the
task period of the primary periodic task in which EtherCAT communications were refreshed.
(b) The refresh cycle of the NX bus of the EtherCAT Slave Terminal is within the task period of
the primary periodic task.
You can check for condition (a) by estimating the task execution time. Refer to Section 5 Designing
Tasks in the NJ-series CPU Unit Software Users Manual (Cat. No. W501-E1-06 or later) for the check-
ing procedure.
You can check for condition (b) from the Sysmac Studio. Refer to Primary Period Setting for Synchro-
nous I/O Refreshing on page 10-10 in 10-3-4 I/O Refreshing Method Operation on page 10-7 for a
detailed checking procedure.
12-1-1 I/O Response Times for Synchronous I/O Refreshing
Prerequisites for Calculations
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