Hx58x EtherCAT®
5 - EtherCAT® interface
5.1 Basic Information on EtherCAT® Protocol
EtherCAT protocol is designed to use the standard Ethernet dataframes for
issuing data; in addition, and as regards the hardware, it is not necessary to
install dedicated masters for establishing and managing the EtherCAT
communication because standard Ethernet network cards can be used. This
results in an advantage in terms of lower costs and simplicity of use because
Ethernet network cards are used in standard personal computers and are easily
commercially available.
An EtherCAT bus can be viewed as a single and large Ethernet device that
receives and sends Ethernet telegrams; it can be considered an Ethernet subnet
supported by an Ethernet dataframes structure.
However this “subnet” must be fitted with one only EtherCAT master controller
and several EtherCAT slaves, but no Ethernet controller with downstream
microprocessor must be present.
Here follows an Ethernet frame structure with EtherCAT:
Inside the Ethernet frames data are transmitted among master and slaves using
PDO (process data objects) protocol. Each PDO message has inside one or more
addresses for issuing data to slaves; data + address/es (and additional elements
such as a validation checksum) joined together forms an EtherCAT telegram
(Datagram).
An EtherCAT frame can contain several telegrams and often a complete control
cycle requires more than one frame.
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