8 EtherCAT Communications
8 - 10
NX-series EtherCAT Coupler Unit User’s Manual (W519)
8-6 Communications between an Ether-
CAT Master and Slaves
This section describes the communications modes between the master and slaves for EtherCAT com-
munications, and the communications modes for EtherCAT Slave Terminals.
In this mode, the slave processes the I/O (i.e., refreshes the I/O data) asynchronous to the communica-
tions cycle of the master.
In this mode, the slave processes the I/O (i.e., refreshes the I/O data) in synchronization with the com-
munications cycle of the master. In this mode, a mechanism called a distributed clock (DC) is used to
synchronize EtherCAT communications. The clock is shared by the master and the slaves. In DC
Mode, the master and slaves are synchronized by sharing the same clock. Interruptions to synchronize
timing are generated in the slaves at precise intervals based on this clock. Interruptions (Sync0) are
generated in the slaves at precise intervals based on this clock. Each slave executes I/O processing at
this precise time.
EtherCAT Slave Terminals support the following two communications modes.
• Free-Run Mode
•DC Mode
Refer to Section 10 I/O Refreshing for information on the operation of an EtherCAT Slave Terminal in
different communications modes.
The communications cycle is determined by the setting for it in the EtherCAT master.
Refer to 3-1-2 EtherCAT Coupler Unit Specifications on page 3-2 for the DC Mode communications
cycles that are supported by the EtherCAT Slave Terminals. There are no specific restrictions for the
Free-Run Mode communications cycles that are supported by the EtherCAT Slave Terminals.
Refer to the NJ-series CPU Unit Built-in EtherCAT Port User’s Manual (Cat. No. W505) for the commu-
nications cycles that are supported by the built-in EtherCAT ports on NJ-series CPU Units.
8-6-1 Communications Modes for Communications between an Ether-
CAT Master and Slaves
Free-Run Mode
DC Mode
8-6-2 Communications Modes for EtherCAT Slave Terminals
8-6-3 Communications Cycle
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