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Chapter 4
Digital Input/Output and PFI
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) × 25 ns (approximately 107 seconds) before it expires. When a watchdog timer expires,
analog output, digital output, and counter output changes may be configured to transition to an
expiration state.
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.
Getting Started with DO Applications in Software
You can use the cDAQ chassis in the following digital output applications:
•
Single-point (on-demand) generation
•
Finite generation
•
Continuous generation
For more information about programming digital output applications and triggers in software,
refer the
LabVIEW Help
or to the
NI-DAQmx Help
.
Digital Input/Output Configuration for NI 9401
When you change the configuration of lines on a NI 9401 digital I/O module between input and
output, NI-DAQmx temporarily reserves all of the lines on the module for communication to
send the module a line configuration command. For this reason, you must reserve the task in
advance through the DAQmx Control Task before any task has started. If another task or route
is actively using the module, to avoid interfering with the other task, NI-DAQmx generates an
error instead of sending the line configuration command. During the line configuration
command, the output lines are maintained without glitching.