4-6 | ni.comChapter 4 Digital Input/Output and PFIUsing an Analog SourceSome C Series modules can generate a trigger based on an analog signal. In NI-DAQmx, this iscalled the Analog Comparison Event.When you use an analog trigger source, the acquisition stops on the first rising or falling edge ofthe Analog Comparison Event signal, depending on the trigger properties.Note Depending on the C Series module capabilities, you may need two modulesto utilize analog triggering.Routing DI Reference Trigger Signal to an Output TerminalYou can route DI Reference Trigger to any output PFI terminal. Reference Trigger is active highby default.DI Pause Trigger SignalYou can use the DI Pause Trigger (di/PauseTrigger) signal to pause and resume a measurementacquisition. The internal sample clock pauses while the external trigger signal is active andresumes when the signal is inactive. You can program the active level of the pause trigger to behigh or low.Using a Digital SourceTo use DI Pause Trigger, specify a source and a polarity. The source can be either from PFI orone of several other internal signals on your cDAQ chassis. Refer to the Device Routing in MAXtopic in the NI-DAQmx Help or the LabVIEW Help for more information.Using an Analog SourceSome C Series modules can generate a trigger based on an analog signal. In NI-DAQmx, this iscalled the Analog Comparison Event.When you use an analog trigger source, the internal sample clock pauses when the AnalogComparison Event signal is low and resumes when the signal goes high (or vice versa).Note Depending on the C Series module capabilities, you may need two modulesto utilize analog triggering.Note Pause triggers are only sensitive to the level of the source, not the edge.Digital Input FiltersWhen performing a hardware-timed task, you can enable a programmable debouncing filter onthe digital input lines of a parallel DIO module. All lines on a module must share the same filterconfiguration. When the filter is enabled, the chassis samples the inputs with a user-configuredFilter Clock derived from the chassis timebase. This is used to determine whether a pulse ispropagated to the rest of the system. However, the filter also introduces jitter onto the inputsignal.
