4 EtherCAT Communications
4 - 10
CJ-series EtherCAT Slave Units Operation Manual (W541)
4-6 Communications Performance
This section describes the PDO I/O response times and the message response times for the EtherCAT
Slave Unit.
This section describes the method for calculating the maximum I/O response time of the EtherCAT
Slave Unit.
The I/O response time is the time from when the CJ-series CPU Unit processes the output data from
the EtherCAT master until the EtherCAT master inputs the processed result.
A timing chart for the I/O response time is provided in the figure below. Use this timing chart with the
provided formula to determine the maximum I/O response time.
4-6-1 I/O Response Time
Timing Chart for I/O Response Time
Element Description
Tmaster
*1
*1. The cycle time of the EtherCAT master is based on the assumption that the EtherCAT master cycle is the
same as the cycle of process data communication. Refer to the EtherCAT master manual about the relation-
ship between these cycles.
Cycle time of the EtherCAT master.
Tslave Processing time of the EtherCAT Slave Unit.
Tcj_plc Cycle time of the CJ-series CPU Unit.
Ttrans Transmission time of the EtherCAT master.
Tmaster
*1
COM PG
SYS I/O
Tcj_plc
COM PG
SYS I/O
2 x Tslave
Tcj_plc
Tcj_plc
Tslave
EtherCAT master
cycle
Tmaster
*1
Cycle of
process data
communication
Ttrans
Ttrans
EtherCAT slave
processing
cycle
2 x Tslave
COM: Overseeing processing
PG: Program execution
SYS: Peripheral processing
I/O: I/O refreshing
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