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3
Basics of communication
3.1
EtherCAT basics
Basic information on the EtherCAT fieldbus can be found in the EtherCAT system documentation.
3.2
Watchdog setting
General information on watchdog settings
The ELxxxx Terminals and EPxxxx Box Modules are equipped with a safety device (watchdog) that switches
the outputs to a safe state after a time that can be preset, for example in the case of interrupted process data
traffic, or to OFF, for example depending on device and setting.
The EtherCAT Slave Controller (ESC) has two watchdogs:
• SM watchdog (default: 100 ms)
• PDI watchdog (default: 100 ms)
SM Watchdog (SyncManagerWatchdog)
The SyncManager watchdog is reset after each successful EtherCAT process data communication with the
terminal/box. If no EtherCAT process data communication takes place with the terminal/box for longer than
the set and activated SM watchdog time, e.g. in the event of a line interruption, the watchdog is triggered and
the outputs are set to FALSE. The OP status of the terminal/box is unaffected by this. The watchdog is only
reset after a successful EtherCAT process data access. Set the monitoring time as specified below.
The SyncManager watchdog monitors correct and timely process data communication with the ESC from the
EtherCAT side.
PDI watchdog (process data watchdog)
If no PDI communication with the EtherCAT slave controller (ESC) takes place for longer than the set and
activated PDI watchdog time, this watchdog is triggered.
PDI (Process Data Interface) is the internal interface between the ESC and local processors in the EtherCAT
slave, for example. The PDI watchdog can be used to monitor this communication for failure.
The PDI watchdog monitors correct and timely process data communication with the ESC but from the
application side.
The SM and PDI watchdogs should be set separately for each slave in the TwinCAT System Manager:
EP3356-0022
Version: 1.1.0
Basics of communication
17
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