Omron CJ1W- ECT21, Operation Manual

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4 EtherCAT Communications
4 - 12 CJ-series EtherCAT Slave Units Operation Manual (W541)
This section describes the method for calculating the minimum SDO message response time of the
EtherCAT Slave Unit.
The message response time is the time from when the EtherCAT master sends the SDO data with the
mailbox until it receives the SDO response from the target EtherCAT Slave Unit.
A timing chart for the SDO message response time is provided in the figure below. Use this timing chart
with the provided formula to determine the minimum SDO message response time.
A formula is provided below to calculate the SDO message response time.
*1. If Tmaster divides the Ts_resp evenly, there is no need to add 1 in the formula.
*2. If 512 divides the data byte size of the message response evenly, there is no need to add 1.
The elements used in the minimum SDO message response time formula are described below. Units of
these elements 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.
 Ts_resp
This is the time from when the message request is received until the EtherCAT Slave Unit completes
generating the response.
4-6-2 SDO Message Response Time
Timing Chart for SDO Message 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.
Ts_resp EtherCAT Slave Unit message response time is 2 ms.
Minimum SDO Message Response Time Formula
Send requesting
SDO
Cycle of
process data
communication
Tmaster
*1
EtherCAT master cycle
Receive
requesting SDO
Ts_resp
Response data
preparation completed
Tmaster
*1
Minimum SDO Message Response Time = (((Ts_resp / Tmaster) + 1 *1 ) x Tmaster) + (((data byte size of
response message / 512) + 1 *2 ) x Tmaster) + Tmaster