Beckhoff EL3681 Documentation page 28

Basics communication
Fig. 9: eEtherCAT tab -> Advanced Settings -> Behavior -> Watchdog
Notes:
• the Multiplier Register 400h (hexadecimal, i. e. x0400) is valid for both watchdogs.
• each watchdog has its own timer setting 410h or 420h, which together with the Multiplier results in a
resulting time.
• important: the Multiplier/Timer setting is only loaded into the slave at EtherCAT startup if the checkbox
in front of it is activated.
• if it is not checked, nothing is downloaded and the setting located in the ESC remains unchanged.
• the downloaded values can be seen in the ESC registers x0400/0410/0420: ESC Access -> Memory
SM watchdog (SyncManager Watchdog)
The SyncManager watchdog is reset with each successful EtherCAT process data communication with the
terminal. If, for example, no EtherCAT process data communication with the terminal takes place for longer
than the set and activated SM watchdog time due to a line interruption, the watchdog is triggered. The status
of the terminal (usually OP) remains unaffected. The watchdog is only reset again by a successful EtherCAT
process data access.
The SyncManager watchdog is therefore a monitoring for correct and timely process data communication
with the ESC from the EtherCAT side.
The maximum possible watchdog time depends on the device. For example, for "simple" EtherCAT slaves
(without firmware) with watchdog execution in the ESC it is usually up to 170 seconds. For complex
EtherCAT slaves (with firmware) the SM watchdog function is usually parameterized via Reg. 400/420 but
executed by the µC and can be significantly lower. In addition, the execution may then be subject to a certain
time uncertainty. Since the TwinCAT dialog may allow inputs up to 65535, a test of the desired watchdog
time is recommended.
28 Version: 3.0 EL3681