© National Instruments Corporation 25 NI cDAQ-9178/9174 User Guide and Specifications
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog signal. In NI-DAQmx, this is
called the Analog Comparison Event.
When you use an analog trigger source, the acquisition stops on the first rising or falling edge of the
Analog Comparison Event signal, depending on the trigger properties.
Routing DI Reference Trigger Signal to an Output Terminal
You can route di/ReferenceTrigger to any output PFI terminal. Reference Trigger is active high by
default.
DI Pause Trigger Signal
You can use the DI PauseTrigger (di/PauseTrigger) 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/PauseTrigger, specify a source and a polarity. The source can be either from PFI or one of
several other internal signals on your NI cDAQ-9178/9174 chassis. Refer to the Device Routing in MAX
topic in the NI-DAQmx Help or the LabVIEW Help for more information.
The NI-DAQmx Help is available after installation from Start»All Programs»National Instruments»
NI-DAQ»NI-DAQmx Help. To view the LabVIEW Help, select Help»Search the LabVIEW Help in
LabVIEW. Alternately, to download the LabVIEW Help, go to
ni.com/manuals.
Using an Analog Source
Some C Series I/O modules can generate a trigger based on an analog signal. In NI-DAQmx, this is
called the Analog Comparison Event.
When you use an analog trigger source, the internal sample clock pauses when the Analog Comparison
Event signal is low and resumes when the signal goes high (or vice versa).
Note Pause triggers are only sensitive to the level of the source, not the edge.
Digital Input Timing Signals
DI Sample Clock Signal
Use the DI Sample Clock (di/SampleClock) signal to sample digital I/O on any slot using
hardware-timed digital modules, and store the result in the DI waveform acquisition FIFO. If the
NI cDAQ-9178/9174 chassis receives a di/SampleClock signal when the FIFO is full, it reports an
overflow error to the host software.
DI Sample Clock
A sample consists of one reading from each channel in the DI task. di/SampleClock signals the start of
a sample of all digital input channels in the task. di/SampleClock can be generated from external or
internal sources as shown in Figure 16.
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