User Guide

NI cDAQ-9172 User Guide and Specifications 30 ni.com
One property of buffered I/O operations is sample mode. The sample mode
can be either finite or continuous:
• Finite—Finite sample mode generation refers to the generation of a
specific, predetermined number of data samples. After the specified
number of samples is written out, the generation stops.
• Continuous—Continuous generation refers to the generation of an
unspecified number of samples. Instead of generating a set number of
data samples and stopping, a continuous generation continues until
you stop the operation. There are three different continuous generation
modes that control how the data is written. These modes are
regeneration, onboard regeneration, and non-regeneration:
– In regeneration mode, you define a buffer in host memory. The
data from the buffer is continually downloaded to the FIFO to be
written out. New data can be written to the host buffer at any time
without disrupting the output.
– With onboard regeneration, the entire buffer is downloaded to the
FIFO and regenerated from there. After the data is downloaded,
new data cannot be written to the FIFO. To use onboard
regeneration, the entire buffer must fit within the FIFO size. The
advantage of using onboard regeneration is that it does not require
communication with the main host memory once the operation is
started, which prevents problems that may occur due to excessive
bus traffic or operating system latency.
– With non-regeneration, old data is not repeated. New data must
continually be written to the buffer. If the program does not write
new data to the buffer at a fast enough rate to keep up with the
generation, the buffer underflows and causes an error.
Analog Output Triggering
Analog output supports two different triggering actions:
• Start trigger
• Pause trigger
An analog or digital trigger can initiate these actions. Any C Series
correlated digital module in slots 5 and/or 6 can supply a digital trigger, and
some C Series analog modules can supply an analog trigger. For more
information refer to the AO Start Trigger Signal section of this document
or to the documentation included with your C Series I/O module(s).