Frequency Generation; Continuous Buffered Sample Clocked Pulse Train Generation; Using The Frequency Generator - National Instruments cRIO-904 Series User Manual

Figure 81. Finite Buffered Sample Clocked Pulse Train Generation
Counter Armed
Sample
Clock
Counter
2 1 0 1 0 1 0 1 0 2 1 0 2 1 0 2 1 0 2 1 0 1 0 1 0 2 1 0 2 1 0
Load Values
Source
Out
3 2 2 2 3 3 3 3 2 2 3 3
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 is not 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 underflows and causes an error.

Continuous Buffered Sample Clocked Pulse Train Generation

This function generates a continuous train of pulses with variable idle and active times. Instead
of generating a set number of data samples and stopping, a continuous generation continues
until you stop the operation. Each point you write specifies pulse specifications that are
updated with each sample clock. When a sample clock occurs, the current pulse finishes
generation and the next pulse uses the next sample specifications.

Frequency Generation

You can generate a frequency by using a counter in pulse train generation mode or by using
the frequency generator circuit, as described in the Using the Frequency Generator section.

Using the Frequency Generator

The frequency generator can output a square wave at many different frequencies. The
frequency generator is independent of the four general-purpose 32-bit counter/timer modules
on the cRIO controller.
The following figure shows a block diagram of the frequency generator.
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