Omron SYSMAC FH Series User Manual page 68

2 Methods for Connecting and Communicating with External Devices
Types of EtherCAT Communications
The following 2 types of communications are available with EtherCAT.
PDO communications are processed in each EtherCAT communication cycle to refresh data continu-
ously. SDO communications are processed between PDO communications.
l Process Data Communications (PDO Communications)
The process data communication function (PDO communications) cyclically transfers process data
in real-time.
The EtherCAT master maps the logical process data space to the nodes to achieve cyclic commu-
nications between the EtherCAT master and slaves.
EtherCAT master
Ethernet frame
Logical process data
Data a
Data b
Data c
l Mailbox Communications (SDO Communications)
The mailbox communication function (SDO communications) is used to perform message commu-
nication.
Whenever necessary, the EtherCAT master sends a command to a slave, and then the slave re-
turns 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
2 - 6
Slave
Ether
Ethernet 1st EtherCAT
CAT
header telegram
header
FH/FHV Series Vision System User's manual for Communication Settings (Z342-E1)
Slave Slave
2nd EtherCAT 3rd EtherCAT
telegram telegram
Slave
CRC