Advantech PCM-26R1EC, User Manual

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PCM-26R1EC User Manual 2
1.1 EtherCAT Introduction
EtherCAT is a high-performance, Ethernet-based fieldbus industrial network system.
The protocol is standardized in IEC 61158 and applies to automation applications
requiring faster and more efficient communications. Short data update times with pre -
cise synchronization make EtherCAT suitable for applications requiring real-time
automation.
1.1.1 EtherCAT
1.1.1.1 The Functional Principle of EtherCAT
EtherCAT is a real-time, high-speed, and flexible Ethernet-based protocol. In an Eth -
erCAT network, the master node sends Ethernet frames via all of the slave nodes.
Under the EtherCAT protocol, standard Ethernet packets or frames are no longer
received, interpreted, or copied as process data at every node. Instead, slave
devices read only the data addressed to them, and the input data are inserted simul -
taneously as the telegram passes through the device, thus processing data “on the
fly.” Typically, the entire network can be addressed with just one frame. Compared
with other Ethernet-based communication protocols, EtherCAT is more efficient in uti -
lizing the available full-duplex bandwidth.
Figure 1.1 The Functional Principle of EtherCAT
1.1.1.2 The EtherCAT Protocol
Data exchanges are cyclically updated between EtherCAT master and slave nodes.
Data in EtherCAT frames are transported directly within the standard IEEE 802.3
Ethernet frame by using Ethertype 0x88a4, and they are processed by the EtherCAT
slave controller on the fly. Each EtherCAT datagram is a command comprising a
header, data, and a working counter (WKC). The datagram header indicates what
type of access the master device requires:

Read, write, read / write

Access to a specified slave device through direct addressing

Access to multiple slave devices through logical addressing
Logical addressing is used for the cyclical exchange of process data. The header and
data are used to specify the operation that the slave must perform, and the WKC is
updated by the slave to inform the master that a slave has processed the command.