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Protocol
The EtherCAT protocol is optimized for process data and is either transported directly in the Ethernet frame
or packed into UDP/IP datagrams. The UDP version is used in situations where EtherCAT segments in other
subnets are addressed via routers. Ethernet frames may contain several EtherCAT telegrams, with each
telegram serving a particular memory area of the logical process image with a size of up to 4 GB. The data
sequence is independent of the physical order of the EtherCAT terminals in the network; addressing can be
in any order. Broadcast, Multicast and communication between slaves are possible. The protocol can also
handle parameter communication, which typically is acyclical.
Performance
EtherCAT reaches new dimensions in network performance. The update time for the data from 1.000
distributed inputs/outputs is only 30 µs - including terminal cycle time. Up to 1.486 bytes of process data can
be exchanged with a single Ethernet frame - this is equivalent to almost 12.000 digital inputs and outputs.
The transfer of this data quantity only takes 300 µs.
Topology
Line, tree or star: EtherCAT supports almost any topology. The bus or line structure known from the
fieldbuses thus also becomes available for Ethernet. Particularly useful for system wiring is the combination
of line and junctions or stubs. The required interfaces exist on the couplers; no additional switches are
required. Naturally, the classic switch-based Ethernet star topology can also be used.
2.1
EtherCAT Highlights
Performance
• 256 digital-I/Os in 12 µs
• 1.000 digital-I/Os in 30 µs
Topology
• line, tree or star topology
• up to 65,535 devices
• network size: almost unlimited (> 500 km)
• operation with or without switches
• cost-effective cabling: Industrial Ethernet patch
cable (CAT5)
Address space
• network-wide process image: 4 Gbyte
• device process image: 1 bit to 64 kbyte
Protokoll
• optimised protocol directly within the Ethernet
frame
• fully hardware-implemented
• for routing and socket interface: UDP datagram
• processing while passing
CXxxxx-B110
• 200 analog-I/Os (16 Bit) in 50 µs,
corresponding to 20-kHz sampling rate
• 100 servo axes every 100 µs
• 12,000 digital I/Os in 350 µs
• twisted pair physical layer:
• Ethernet 100BASE-TX, up to 100 m between 2
devices
• alternative: fibre-optic cable variants 50 to
2,000 m
• hot connect/disconnect of bus segments
• address allocation: freely configurable
• device address selection: automatically via
software
• distributed clock for accurate synchronisation
• time stamp data types for resolution in the
nanosecond range
• oversampling data types for high-resolution
measurements
Version: 1.3
System overview EtherCAT
9
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