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DI Pause Trigger Signal

You can use the DI Pause Trigger signal to pause and resume a measurement acquisition. The

internal sample clock pauses while the external trigger signal is active and resumes when the

signal is inactive. You can program the active level of the pause trigger to be high or low.

Using a Digital Source

To use DI Pause Trigger, specify a source and a polarity. The source can be either from PFI or

one of several other internal signals on your cRIO controller. Refer to the "Device Routing in

MAX" topic in the NI-DAQmx Help or the LabVIEW Help for more information.

Digital Input Filters

When performing a hardware timed task, you can enable a programmable debouncing filter on

the digital input lines of a parallel DIO module. All lines on a module must share the same

filter configuration. When the filter is enabled, the controller samples the inputs with a user-

configured Filter Clock derived from the controller timebase. This is used to determine

whether a pulse is propagated to the rest of the system. However, the filter also introduces

jitter onto the input signal.

In NI-DAQmx, the filter is programmed by setting the minimum pulse width, Tp

, that will

pass the filter, and is selectable in 25 ns increments. The appropriate Filter Clock is selected by

the driver. Pulses of length less than 1/2 Tp will be rejected, and the filtering behavior of

lengths between 1/2 Tp and 1 Tp are not defined because they depend on the phase of the

Filter Clock relative to the input signal.

The figure below shows an example of low-to-high transitions of the input signal. High-to-low

transitions work similarly.

Assume that an input terminal has been low for a long time. The input terminal then changes

from low to high, but glitches several times. When the filter clock has sampled the signal high

on consecutive rising edges, the low-to-high transition is propagated to the rest of the circuit.

Figure 41. Filter Example

Digital Input P0.x

Filter Clock

Filtered Input

1 1 21 1 21

Getting Started with DI Applications in Software

You can use the cRIO controller in the following digital input applications:

• Single-point acquisition

• Hardware-Timed Single Point acquisition

Tp is a nominal value; the accuracy of the controller timebase and I/O distortion will affect this

value.

National Instruments cRIO-904 Series User Manual

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