Lika H 58 Series, Руководство пользователя

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Hx58x EtherCAT®
5.1.1 Data transfer
Usually, in a data bus system, master controller sends online a data request and
then waits for data to be processed and sent back from each slave node; this
does not comply with a real-time system because master receives data from
slaves in different moments and the whole system cannot be synchronized.
In EtherCAT the real-time characteristic of the system is quite improved because
data are processed “on-the-fly”, using one single frame to acquire all data from
all slaves.
In fact the frame sent by the master is read by each slave node data is addressed
to while the telegram passes through the device; similarly, input data is inserted
while the telegram passes through. Then the telegram is forwarded to the next
device. Telegrams are only delayed by a few nanoseconds.
The last slave issues back the complete frame to the master with all the
requested data (again passing through all the slaves).
This efficient data flow is guaranteed by the 100BASE-TX full-duplex structure
of EtherCAT bus which is fitted with two separated lines for transmitting and
receiving data.
Moreover the protocols exchange takes place inside the hardware and it is thus
independent from CPU and software processing.
5.1.2 ISO/OSI Layer model
* “empty” means that the layer behaviour exists, but is not shown explicitly.
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