[quote]EtherCAT UDP packages the EtherCAT proto-
Particularly useful for system wiring is the combination
of line and branches or stubs: the required interfaces
exist on many devices (e.g. on I/O modules); no additional
switches are required. Naturally, the classic switch-based
Ethernet star topology can also be used.
Wiring flexibility is further maximized through the
choice of different cables. Flexible and inexpensive standard
Ethernet cables transfer the signals in 100BASE-TX
mode. Plastic optical fibers (POF) will complement the system
for special applications. The complete choice of Ethernet
wiring – such as different optical fibers and copper cables
– can be used in combination with switches or media
The Fast Ethernet physics (100BASE-TX) enables a cable
length of 100 m between two devices. Since up to 65,535
devices can be connected, the size of the network is almost
The Ethernet protocol according to IEEE 802.3 remains
intact right up to the individual device; no sub-bus is required.
In order to meet the requirements of a modular device
like an electronic terminal block, the physical layer in
the coupling device can be converted from twisted pair or
optical fiber to LVDS (alternative Ethernet physical layer,
standardized in [4,5]). A modular device can thus be extended
very cost-efficiently. Subsequent conversion from
the backplane physical layer LVDS to the 100BASE-TX physical
layer is possible at any time – as usual with Ethernet.
■ Figure 4: EtherCAT: Standard Frames according to IEEE 802.3 
munication between controllers (master/master). Freely
addressable network variables for process data and a variety
of services for parameterization, diagnosis, programming
and remote control cover a wide range of requirements.
The data interfaces for master/slave and master/
master communication are identical.
For slave-to-slave communication, two mechanisms
are available. Upstream devices can communicate to
downstream devices within the same cycle – and thus extremely
fast. Since this method is topology-dependent, it is
particularly suitable for slave-to-slave communication relationships
given by machine design – e.g. in printing or
packaging applications. For freely configurable slave-toslave
communication, the second mechanism applies: the
data is relayed by the master. Here, two cycles are needed,
but due to the extraordinary performance of EtherCAT this
is still faster than any other approach.
EtherCAT only uses standard frames according to  –
the frames are not shortened. EtherCAT frames can thus be
sent from any EthernetMAC, and standard tools (e.g. monitor)
can be used.
Line, tree or star: EtherCAT supports almost any topology
(see Fig. 5). The bus or line structure known from the fieldbuses
thus also becomes available for Ethernet, without
the quantity limitations implied by cascaded switches or
col into UDP/IP datagrams (see Fig. 4). This enables any
control with Ethernet protocol stack to address EtherCAT
Isn’t it only UDP?