Ethercat Introduction; Ethercat - Advantech AMAX-4800 Series User Manual

1.1

EtherCAT Introduction

EtherCAT (Ethernet Control Automation Technology) is a high-performance,
Ethernet-based fieldbus industrial network system. The protocol is standardized in
IEC 61158 and applied to automation applications that require fast and efficient com-
munications. Short data update times with precise synchronization make EtherCAT
suitable for real-time automation technology requirements.
1.1.1

EtherCAT

Functional Principle
EtherCAT is a flexible, real-time, high-speed, Ethernet-based protocol. In EtherCAT
networks, the master sends Ethernet frames through all the slave nodes. However,
standard Ethernet packets or frames are no longer received, interpreted, and copied
as process data at every node. Instead, slave devices read the data addressed to
them while inserting input data as the telegram passes through the device, effectively
processing data immediately. Typically, the entire network can be addressed using a
single frame. Compared with other Ethernet-based communication solutions, Ether-
CAT uses the full available duplex bandwidth more efficiently.
1.1.1.1 Protocol
Data exchanges are cyclically updated between the EtherCAT master and slaves.
Data in EtherCAT frames is transported within the standard IEEE 802.3 Ethernet
frame using EtherType 0x88a4 and then processed by the EtherCAT slave controller.
Every EtherCAT datagram is a command that consists of a header, data, and a work-
ing counter. The datagram header indicates the type of access requested by the
master device (see the examples listed below).
 Read, write, read-write
 Access to a specific 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. The working
counter is updated by the slave to notify the master that the command has been pro-
cessed.
Every EtherCAT datagram ends with a 16-bit working counter (WKC). The WKC
counts the number of devices successfully addressed by the EtherCAT datagram.
AMAX-4800 User Manual
Figure 1.1 EtherCAT Function Principle
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