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4 EtherCAT Communications
CJ-series EtherCAT Slave Units Operation Manual (W541)
4-6 Communications Performance
4
4-6-1 I/O Response Time
A formula is provided below to calculate the I/O response time.
The elements used in the maximum I/O response time formula are described below. Units of these ele-
ments are in ms.
Tmaster
The cycle time of the EtherCAT master is assumed to be the same as the process data communica-
tion cycle. Use the process data communication cycle that is set in the EtherCAT master.
Tslave
The EtherCAT Slave Unit processing time can be calculated with the formula below.
Units of IN and OUT data area size are in channels (CH).
Tcj_plc
The PLC cycle time can be obtained by referring to the CPU Unit’s operation manual.
The I/O refresh time of the PLC is the maximum time required for I/O data to be exchanged between
the CPU Unit and the EtherCAT Slave Unit. The PLC cycle time is increased when an EtherCAT
Slave Unit is mounted as shown in the formula below.
Units of IN and OUT data area size are in channels (CH).
Use the values of A and B in table below for the CPU type that has the EtherCAT Slave Unit
mounted.
Ttrans
The transmission time of the EtherCAT master can be calculated with the formula below.
The number of EtherCAT slaves represents the number of EtherCAT slaves that are present on the
same EtherCAT network. An EtherCAT Slave Unit is considered to be one EtherCAT slave.
The EtherCAT frame length in bytes represents the data byte size of the EtherCAT frame on the
same EtherCAT network.
I/O Response Time Formula
CPU type Value of A Value of B
CJ1M 0.3 0.0008
CJ2H 0.3 0.0024
CJ2M 0.3 0.0024
Maximum I/O Response Time = Tmaster + (4 x Tslave) + (2 x Tcj_plc) + (2 x Ttrans)
Tslave = 1.5 + (0.0007 x (IN data area size + OUT data area size))
I/O Refresh Time = A + (B x (IN data area size + OUT data area size))
Ttrans = ((1.24 x Number of EtherCAT slaves) + (0.09 x EtherCAT frame length in bytes)) / 1000
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