© National Instruments
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6-23
Watchdog Timer
The watchdog timer is a software-configurable feature used to set critical outputs to safe states
in the event of a software failure, a system crash, or any other loss of communication between
the application and the X Series device.
Note
The NI-DAQmx Watchdog feature is meant to protect a system from
software errors and hangs. In the case of a PXI system with remote control through
MXI, a lost MXI connection could result in unexpected Watchdog behavior and
therefore improperly implemented Watchdog states.
When the watchdog timer is enabled, if the X Series device does not receive a watchdog reset
software command within the time specified for the watchdog timer, the outputs go to a
user-defined safe state and remain in that state until the watchdog timer is disarmed by the
application and new values are written, the device is reset, or the computer is restarted. The
expiration signal that indicates an expired watchdog will continue to assert until the watchdog is
disarmed. After the watchdog timer expires, the device ignores any digital writes until the
watchdog timer is disarmed.
Note
When the watchdog timer is enabled and the computer enters a fault
condition, ports that are set to tri-state remain tri-stated and do not go to user-defined
safe states.
You can set the watchdog timer timeout period to specify the amount of time that must elapse
before the watchdog timer expires. The counter on the watchdog timer is configurable up to
(2
32
- 1) × 8 ns (approximately 34 seconds) before it expires. A watchdog timer can be set for all
DIO and PFI lines.
Summary of Contents for 6368
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