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Overview of EtherCAT
EtherCAT does not send data to individual slave nodes on the network, instead,
it passes Ethernet frames through all of the slave nodes.
When frame passes through a slave node, the slave node reads and writes data
in the areas allocated to it in the Ethernet frames in a few nanoseconds.
Ethernet frames sent from the EtherCAT master unit go through all the
EtherCAT slave unit without stopping on the way. Once they reach the final
slave unit, they are sent back from the final slave unit, pass through all slave
units again, and return to the EtherCAT master unit.
Communications Types of EtherCAT
EtherCAT provides the two types of communication functions of PDO
communications and SDO communications.
PDO communications constantly update the data every communication cycle on
EtherCAT, and SDO communications are processed in between those updates.
(1)
Process data communications functions (PDO communications)
This communication function is used to transfer process data in a fixed
cycle.
By mapping logical process data space to each node by the EtherCAT
master unit, it achieves fixed-cycle communications among the EtherCAT
master unit and slave units.
(2)
Mailbox communications functions (SDO communications)
This refers to message communications in EtherCAT communications.
The EtherCAT master unit transmits commands to slave units and the
slave units return responses to the EtherCAT master unit at any timing.
EtherCAT master
unit
Slave unit
Slave unit
OUT
IN
Ethernet frame
• Reading output data addressed
to the local slave units
• Writing input data
Summary of Contents for MG80-EC
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