BECKHOFF DK9222-0211-0021 - Manual (Page 4)

I/O
XFC
Application Note DK9222-0211-0021
in the identical system time being present in the entire network. In addition, the controller/PLC is also synchronized, as a result
of which the fieldbus clock with the I/O update is synchronous to the PLC.
The exact temporal assignment of the events takes place on this uniform timebase. The process data no longer consist only
of user data; they additionally have a time stamp containing the concrete time of the event. The time stamp is a 64-bit value
with a resolution of 1 ns, which enables a significantly more detailed temporal reference of the process data and releases the
process information from the PLC cycle. With typical plant sizes, the performance of EtherCAT is so high that signals collected
from the field are available to the controller even before a new computing cycle is started. Hence, a short reaction time is
already possible in the next cycle.
Influence on input signals
Due to this time stamp principle, event recognition is released from the coarse pattern of the cycle clock and can be resolved
with the much finer pattern of 1 ns without increasing the system load.
time stamp
06.12.10 16.45 pm 36 s 279 ms 123 µs 546 ns
real-time
changing edge at the digital input
Temporal assignment with time stamp
PLC time
EtherCAT
Fig. 5 Temporal classification by time stamp
Influence on output signals
The time stamp principle is also used to trigger events, since the identical criteria of the temporal assignment exist here and
the switching of output signals is also released from the rigid pattern of the cycle time. If a digital output is to be activated
at a defined time X, in order to trigger a cutting procedure on a paper web, for example, an appropriate time stamp is set for
the digital output. The time at which the cutter must be activated is calculated from the temporal relationship between the
transport speed of the paper web and the length of the piece to be cut.
New Automation Technology Beckhoff 4
For application notes see disclaimer on the last page