12 Communications Performance
12 - 22
NX-series EtherCAT Coupler Unit User’s Manual (W519)
12-2 Message Response Time
This section describes the message response time for SDO communications and for NX object
read/write instructions when an EtherCAT Slave Terminal is connected to the built-in EtherCAT port on
an NJ-series CPU Unit.
This section describes the instructions that are used to execute message communications.
Reading and Writing SDO Data
You can read and write SDO data with the following EtherCAT communications instruction to exe-
cute SDO communications.
Reading and Writing NX Objects
You can use the following NX object read/write instructions to read and write NX objects.
The message response time is the time from when the SDO communications instruction or Read NX
Unit Object or Write NX Unit Object instruction is executed in the user program until execution of the
instruction is completed.
When the instruction is executed in the user program, the EtherCAT master sends a frame to the Ether-
CAT Coupler Unit or to an NX Unit in the EtherCAT Slave Terminal through the system service. When
the EtherCAT Coupler Unit and NX Unit receive the frame, they process the message. When the mes-
sage processing is completed, the EtherCAT master receives a response from the EtherCAT Slave Ter-
minal to complete execution of the instruction.
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 EtherCAT Coupler Unit is not processing any of the following high-load processes.
• Multiple message communications
• Error processing
12-2-1 Special Instructions
Function name Instruction Description
Read EtherCAT CoE SDO EC_CoESDORead Sets the parameters and reads data from the object
dictionary (SDO data) in the EtherCAT Slave Terminal.
Write EtherCAT CoE SDO EC_CoESDOWrite Sets the parameters and writes data to the object dic-
tionary (SDO data) in the EtherCAT Slave Terminal.
Function name Instruction Description
Read NX Unit Object NX_ReadObj Sets the parameters and reads data from the NX
objects in the EtherCAT Slave Terminal.
Write NX Unit Object NX_WriteObj Sets the parameters and writes data to the NX objects
in the EtherCAT Slave Terminal.
12-2-2 Message Response Time
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