Chapter 3
Analog Output
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National Instruments Corporation
3-5
Finite sample mode generation refers to the generation of a specific,
predetermined number of data samples. Once the specified number of
samples has been written out, the generation stops.
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
several different methods of continuous generation that control what data is
written. These methods are regeneration, FIFO regeneration, and
non-regeneration modes.
Regeneration is the repetition of the data that is already in the buffer.
Standard regeneration is when data from the PC buffer is continually
downloaded to the FIFO to be written out. New data can be written to the
PC buffer at any time without disrupting the output.
With FIFO regeneration, the entire buffer is downloaded to the FIFO and
regenerated from there. Once the data is downloaded, new data cannot be
written to the FIFO. To use FIFO regeneration, the entire buffer must fit
within the FIFO size. The advantage of using FIFO regeneration is that it
does not require communication with the main host memory once the
operation is started, thereby preventing any problems that may occur due to
excessive bus traffic.
With non-regeneration, old data will not be repeated. New data must be
continually 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
will underflow and cause an error.
Non-Buffered
In hardware-timed non-buffered generations, data is written directly to the
FIFO on the device. Typically, hardware-timed non-buffered operations
are used to write single samples with known time increments between them
and good latency.
Analog Output Triggering
Analog output supports two different triggering actions: start and pause. An
analog or digital hardware trigger can initiate these actions. All E Series
devices support digital triggering, and some also support analog triggering.
Refer to Appendix A,
, to find your device
triggering options.
