Ethercat Communications Overview; Structure Of Can Application Protocol Over Ethercat (Coe) - Omron EJ1 EtherCAT User Manual

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EtherCAT Communications Overview

This section provides an overview of EtherCAT communications.
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Structure of CAN Application Protocol over EtherCAT (CoE)

EtherCAT allows the use of multiple protocols for communications. However, the EtherCAT Slave Unit
uses the CAN application protocol over EtherCAT (CoE) as the device profile for the CAN application
protocol. The CoE is a communications interface that is designed to provide compatibility with Ether-
CAT devices. The CAN application protocol is an open network standard.
The following figure shows how the CoE is structured for an EtherCAT Slave Unit.
EtherCAT Slave Unit
The objects in the object dictionary for the CAN application protocol are broadly divided into PDOs (pro-
cess data objects) and SDOs (service data objects).
PDOs are contained in the object dictionary. The PDOs can be mapped in the object dictionary. The
process data is defined by the PDO mappings. PDOs are used in PDO communications for periodic
exchange of process data.
SDOs are the objects that can be read and written. SDOs are used in non-periodic SDO communica-
tions (event-driven message communications).
If you use the CoE interface to set the object dictionary for PDOs and SDOs, you can provide EtherCAT
devices with the same device profiles as the CAN application protocol.
EJ1 EtherCAT Slave Unit User's Manual (H192)
3 Part Names and EtherCAT Communications Overview
Application layer
SDO (mailbox)
Transitions of
communications states
Registers Mailbox
SyncManager
EtherCAT data link layer
EtherCAT physical layer
Slave application
Object dictionary
PDO mappings
PDO communications (cyclic)
Process data
FMMU
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