Watchdog behavior in case of a bus error

The setting in index 0x80n0:05 “Watchdog” defines how the output should assume a safe state in the event of a bus error. The following table shows the available settings.

Watchdog behavior in case of a bus error 1:Fig.23: PWM watchdog settings in case of a bus error

Desired state
of the output in the event of a bus error

Specification in 0x80n0:05 “Watchdog”
(n = 0 for PWM1, n = 2 for PWM2, n = 4 for PWM3, n = 6 for PWM4)

set to specified value

0: “Default Watchdog Value” (default setting)

  • The duty cycle value specified for the output in the “PWM Duty Cycle” process data value is set to the value defined in index 0x80n0:13 “Default Output”.
  • The frequency value specified for the output in the “PWM Frequency“” process data value is set to the value defined in index 0x80n0:17 “Default Period”.

Notice Please note that the values must be specified as integer variables (see the following example).

0x80n0:13 “Default Output”:
0hex (0dec)                 corresponds to a 0% duty cycle
7FFFhex (32,767dec) corresponds to a 50% duty cycle
FFFFhex (65,535dec) corresponds to a 100% duty cycle

0x80n0:17 “Default Period”:
3E8hex (1000dec) µs corresponds to 1 kHz

set to specified value via ramp

1: “Watchdog ramp”

Using the ramp defined in index 0x80n0:14 “Default Output Ramp” (linear change [digit/ms])

  • the duty cycle value specified for the output in the “PWM Duty Cycle” process data value is set to the value defined in index 0x80n0:13 “Default Output”.
  • the frequency value specified for the output in the “PWM Frequency” process data value is switched to the value defined in index 0x80n0:17 “Default Period”.

Retain current value

2: Last value
The output retains the current state.

Switch to high-resistance
(Tristate)

3: “High impedance”
The output is switched to high-impedance.

Notice

Apply watchdog settings for power supply units that can be configured via EtherCAT

  • If a power supply unit that can be configured via EtherCAT is used for the external power supply – for example, an EL9501 power supply terminal (0…20 V DC, 0…2 A) – the settings on this power supply unit must also be configured according to the requirements.
  • If no external power is supplied in the event of a bus error, no output voltage is generated.

Ramp

You can define the time to reach the default value when the watchdog behavior is set to the value 1 "Watchdog ramp".

 

Watchdog behavior in case of a bus error 2:

t: time in ms until the default value is reached.

ncurrent : the last output value that was received by the controller before the communication interruption.

ndefault : default value (CoE parameter 0x80n0:13).

vramp : ramp velocity in digits/ms (CoE parameter 0x80n0:14).

Tristate

In the event of a bus error, the output can be switched to a tristate state, actively to 24 V and high-impedance. The high-resistance tristate state ensures that the respective output behaves as if it were not connected. This means that the outputs of other outputs/devices connected to this output are not affected. The associated output takes on the same output voltage as the other active devices.

Diagnostics in case of bus error

The triggering of the watchdog event is indicated by:

LED 1: “Run”, LED 2: “Dev error”

Process data

DiagMessages “
” when communication
is resumed

“Run” blinks, “Dev error” lights up red

Watchdog behavior in case of a bus error 3:

–

Text ID: 0x8114 Output Cycle Counter watchdog has triggered

Text ID: 0x8105 PD watchdog has triggered