Omron FH series User Manual page 48

Types of EtherCAT Communications
The following 2 types of communications are available with EtherCAT.
PDO communications are executed in each EtherCAT communications cycle to refresh data continuously. SDO
communications are executed between PDO communications.
Process Data Communications (PDO Communications)
The process data communication function (PDO communication) cyclically transfers process data in real-time.
The EtherCAT master maps the logical process data space to the nodes to achieve cyclic communications
between the EtherCAT master and slaves.
EtherCAT master
Ethernet frame
Ethernet
header
Logical process data
Data a
Data b
Data c
Mailbox Communications (SDO Communications)
The mailbox communication function (SDO communication) is used to perform message communication.
Whenever necessary, the EtherCAT master sends a command to a slave, and then the slave returns a
response to the EtherCAT master.
The mailbox communication function (SDO communication) has the following functions.
• Reading and writing process data
• Setting slaves
• Monitoring slave status
46
EtherCAT Connections (FH-1000 series/FH-3000 series only)
Slave
Slave
Ether
1st EtherCAT 2nd EtherCAT
CAT
telegram
header
Slave
3rd EtherCAT
telegram telegram
Vision System FH/FZ5 Series User's Manual
for Communications Settings (Z342)
Slave
CRC