© National Instruments | 4-7NI cDAQ-9138/9139 User ManualIn NI-DAQmx, the filter is programmed by setting the minimum pulse width, Tp1 , that will passthe filter, and is selectable in 25 ns increments. The appropriate Filter Clock is selected by thedriver. Pulses of length less than 1/2 Tp will be rejected, and the filtering behavior of lengthsbetween 1/2 Tp and 1 Tp are not defined because they depend on the phase of the Filter Clockrelative to the input signal.Figure 4-3 shows an example of low-to-high transitions of the input signal. High-to-lowtransitions work similarly.Assume that an input terminal has been low for a long time. The input terminal then changesfrom low to high, but glitches several times. When the filter clock has sampled the signal highon consecutive rising edges, the low-to-high transition is propagated to the rest of the circuit.Figure 4-3. Filter ExampleGetting Started with DI Applications in SoftwareYou can use the cDAQ controller in the following digital input applications:• Single-point acquisition• Finite acquisition• Continuous acquisitionFor more information about programming digital input applications and triggers in software,refer to the NI-DAQmx Help or the LabVIEW Help for more information.Change Detection EventThe Change Detection Event is the signal generated when a change on the rising or falling edgelines is detected by the change detection task.Routing Change Detection Event to an Output TerminalYou can route ChangeDetectionEvent to any output PFI terminal.Change Detection AcquisitionYou can configure lines on parallel digital modules to detect rising or falling edges. When oneor more of these lines sees the edge specified for that line, the cDAQ controller samples all thelines in the task. The rising and falling edge lines do not necessarily have to be in the task.1 Tp is a nominal value; the accuracy of the controller timebase and I/O distortion will affect this value.Digital Input P0.xFilter ClockFiltered Input1 1 21 1 21
