Basic Principles; System Properties; Fig. 12 Ethercat Telegram Structure - Beckhoff BK11 0 Series Documentation

4

Basic principles

4.1

System properties

Protocol
The EtherCAT protocol is optimized for process data and is transported directly within the Ethernet frame
thanks to a special Ether-type. It may consist of several sub-telegrams, each serving a particular memory
area of the logical process images that can be up to 4 gigabytes in size. The data sequence is independent
of the physical order of the Ethernet terminals in the network; addressing can be in any order. Broadcast,
Multicast and communication between slaves are possible. Transfer directly in the Ethernet frame is used in
cases where EtherCAT components are operated in the same subnet as the control computer.
However, EtherCAT applications are not limited to a subnet: EtherCAT UDP packs the EtherCAT protocol
into UDP/IP datagrams. This enables any control with Ethernet protocol stack to address EtherCAT systems.
Even communication across routers into other subnets is possible. In this variant, system performance
obviously depends on the real-time characteristics of the control and its Ethernet protocol implementation.
The response times of the EtherCAT network itself are hardly restricted at all: the UDP datagram only has to
be unpacked in the first station.
Fig. 12: EtherCAT Telegram Structure
Protocol structure: The process image allocation is freely configurable. Data are copied directly in the I/O
terminal to the desired location within the process image: no additional mapping is required. The available
logical address space is with very large (4 GB).
BK11x0, BK1250 Version: 4.1
Basic principles
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