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 two 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.
Notes:
- the multiplier is valid for both watchdogs.
- each watchdog has its own timer setting, the outcome of this in summary with the multiplier is a resulting time.
- Important: the multiplier/timer setting is only loaded into the slave at the start up, if the checkbox is activated.
If the checkbox is not activated, nothing is downloaded and the ESC settings remain unchanged.
Multiplier
Both watchdogs receive their pulses from the local terminal cycle, divided by the watchdog multiplier:
1/25 MHz * (watchdog multiplier + 2) = 100 µs (for default setting of 2498 for the multiplier)
The standard setting of 1000 for the SM watchdog corresponds to a release time of 100 ms.
The value in multiplier + 2 corresponds to the number of basic 40 ns ticks representing a watchdog tick.
The multiplier can be modified in order to adjust the watchdog time over a larger range.
Example “Set SM watchdog”
This checkbox enables manual setting of the watchdog times. If the outputs are set and the EtherCAT communication is interrupted, the SM watchdog is triggered after the set time and the outputs are erased. This setting can be used for adapting a terminal to a slower EtherCAT master or long cycle times. The default SM watchdog setting is 100 ms. The setting range is 0...65535. Together with a multiplier with a range of 1...65535 this covers a watchdog period between 0...~170 seconds.
Calculation
Multiplier = 2498 → watchdog base time = 1 / 25 MHz * (2498 + 2) = 0.0001 seconds = 100 µs
SM watchdog = 10000 → 10000 * 100 µs = 1 second watchdog monitoring time
CAUTIONThe function for switching off of the SM watchdog via SM watchdog = 0 is only implemented in terminals from version -0016. In previous versions this operating mode should not be used.
CAUTIONIf the SM watchdog is activated and a value of 0 is entered the watchdog switches off completely. This is the deactivation of the watchdog! Set outputs are NOT set in a safe state, if the communication is interrupted.