© National Instruments Corporation 27 NI cDAQ-9178/9174 User Guide and Specifications
Getting Started with DI Applications in Software
You can use the NI cDAQ-9178/9174 chassis in the following digital input applications:
• Single-Point
•Finite
• Continuous
For more information about programming digital input applications and triggers in software, refer to 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.
Change Detection Event
The Change Detection Event is the signal generated when a change on the rising or falling edge lines is
detected by the change detection task.
Routing Change Detection Event to an Output Terminal
You can route ChangeDetectionEvent to any output PFI terminal.
Change Detection Acquisition
You can configure lines on hardware-timed digital modules to detect rising or falling edges. When one
or more of these lines sees the edge specified for that line, the NI cDAQ-9178/9174 samples all the lines
in the task. The rising and falling edge lines do not necessarily have to be in the task.
Change detection acquisitions can be buffered or nonbuffered:
• Nonbuffered Change Detection Acquisition—In a nonbuffered acquisition, data is transferred
from the NI cDAQ-9178/9174 directly to a PC buffer.
• Buffered Change Detection Acquisition—A buffer is a temporary storage in computer memory
for acquired samples. In a buffered acquisition, data is stored in the NI cDAQ-9178/9174 onboard
FIFO then transferred to a PC buffer. Buffered acquisitions typically allow for much faster transfer
rates than nonbuffered acquisitions because data accumulates and is transferred in blocks, rather
than one sample at a time.
Digital Output
To generate digital output, insert a digital output C Series I/O module in any slot on the
NI cDAQ-9178/9174 chassis. The generation specifications, such as the number of channels, channel
configuration, update rate, and output range, are determined by the type of C Series I/O module used.
For more information, refer to the documentation included with your C Series I/O modules.
You can run one hardware-timed digital output task at a time on the NI cDAQ-9178/9174 chassis. At the
same time, you can also run one or more software-timed (single-point) tasks.
For each digital output module, you can either:
• Assign all of the channels on the module to the hardware-timed task.
• Assign all of the channels on the module to one or more software-timed tasks.
Digital Output Data Generation Methods
When performing a digital output operation, you either can perform software-timed or hardware-timed
generations. Hardware-timed generations must be buffered.
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