The EtherCAT data link layer is optimized for the fast transfer of process data. Here it is
specified how the process data of the device are assigned to the EtherCAT process data
and how the application of the device is synchronized to the EtherCAT cycle. The map-
ping of the process data happens by PDO mapping and by Sync-Manager-PDO-Assign
objects. These describe, which objects of the object directory are transferred as object
data via EtherCAT. The cycle time to transfer the process data via EtherCAT and how this
is synchronized for the transfer is specified with the Sync-Manager-Communication
objects.
Via Emergencies diagnostics, process events and errors at state change of the State
Machine may be transferred.
Status messages, which show the current state of the device, should directly be trans-
ferred within the process data.
Due to the run time of an EtherCAT frame at the bus, the outputs of the EtherCAT slave
stations are activated at different times and the inputs are read at different times. For an
isochronous access to the process data EtherCAT provides the "distributed clock" func-
tionality. In EtherCAT "
D
istributed
C
locks" means a logical combination of "clocks", which
are located in the EtherCAT devices With this there is the possibility to locally provide a
synchronized time in each bus device. With DC current output values are activated in
equal time on the slave stations, and the input values read at precisely this time. This
moment is called
Sync
signal. If an EtherCAT device supports the DC, it has its own
clock. After PowerON this first locally works, based on an own pulse generator. By
selecting an EtherCAT slave station, which has to provide the reference time, the distrib-
uted clocks can be synchronized. This
reference clock
so represents the system time.
Process data (PDOs)
Emergencies
Distributed clocks (DC)
VIPA System SLIO
Deployment
Basics EtherCAT > General
HB300 | IM | 053-1EC01 | en | 18-49
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