The watchdog timer is a software-configurable feature used to set critical outputs to expiration states in the event of a software failure, a system crash, or any other loss of communication between the application and the cDAQ chassis.

When the watchdog timer is enabled, if the cDAQ chassis does not receive a watchdog reset software command within the time specified for the watchdog timer, the outputs go to a user-defined expiration state and remain in that state until the watchdog timer is disarmed by a device reset. After the watchdog timer expires, the cDAQ chassis cannot perform any operation until the cDAQ chassis is reset.

You can use the watchdog timer to do the following:

  • Set a timeout period to specify the amount of time that must elapse before the watchdog timer expires
  • Set to expire upon loss of network connectivity

The counter on the watchdog timer is configurable up to (232 - 1) × 25 ns (approximately 107 seconds) before it expires. Analog output, digital output, and counter output channels can be configured to transition to an expiration state when a watchdog timer expires.

Resetting the chassis after a watchdog expiration event results in all module outputs defaulting to power up or startup states as defined in the module specifications.

Note Resetting the chassis after a watchdog expiration event may result in undefined transient behavior on the outputs of the NI-9269 and NI-9474 modules. Consult the module specifications for the expected I/O behavior.
Note Restarting or re-reserving the chassis may lead to undefined transient behavior on the outputs of any modules, so these operations are not recommended as means of a watchdog expiration event recovery.
Note No other operations may be running on the cDAQ chassis while the watchdog timer task is being started; this includes all DAQmx tasks, calibration of modules, and routing and configuration of signals on the chassis. After the watchdog timer task starts, DAQmx tasks can be started and stopped and other operations can be performed.