Basics communication
EL673128 Version: 2.8
4 Basics communication
4.1 EtherCAT basics
Please refer to the EtherCAT System Documentation for the EtherCAT fieldbus basics.
4.2 General notes for setting the watchdog
ELxxxx terminals are equipped with a safety feature (watchdog) that switches off the outputs after a
specifiable time e.g. in the event of an interruption of the process data traffic, depending on the device and
settings, e.g. in OFF state.
The EtherCAT slave controller (ESC) in the EL2xxx terminals features 2 watchdogs:
• SM watchdog (default: 100 ms)
• PDI watchdog (default: 100 ms)
SM watchdog (SyncManager Watchdog)
The SyncManager watchdog is reset after each successful EtherCAT process data communication with the
terminal. If no EtherCAT process data communication takes place with the terminal 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 state of the terminal is unaffected. The watchdog is only reset after a
successful EtherCAT process data access. Set the monitoring time as described 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 from the
application side.
The settings of the SM- and PDI-watchdog must be done for each slave separately in the TwinCAT System
Manager.
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