Omron CJ1W-ECT21 Operation Manual page 107

I/O Response Time Formula
A formula is provided below to calculate the I/O response time.
Maximum I/O Response Time = Tmaster + (4 x Tslave) + ((1 + N) x Tnj_task) + (2 x Tnj_bus) +
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.
Tslave = 1.5 + (0.0007 x (IN data area size + OUT data area size))
Units of IN and OUT data area size are in channels (CH).
 Tnj_task
This is the time that is set for the task period of the primary periodic task in the CPU Unit that is con-
nected to the EtherCAT Slave Unit. The value of N can be found with the following information.
• If the task period is ≤ 1.000 ms, use a value of 2 for N.
• If the task period is ˃ 1.000 ms, use a value of 1 for N.
 Tnj_bus
The I/O bus communication cycle in the NJ-series CPU Unit can be calculated with the formula
below.
Tnj_bus = (Number of CPU Bus Units + 1) / Task period
 Ttrans
The transmission time of the EtherCAT master can be calculated with the formula below.
Ttrans = ((1.24 x Number of EtherCAT slaves) + (0.09 x EtherCAT frame length in bytes)) / 1000
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.
CJ-series EtherCAT Slave Units Operation Manual for NJ-series CPU Unit (W542)
(2 x Ttrans) + (2 x Tnj_refresh)
4 EtherCAT Communications
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