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2-11
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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. Use the NI-DAQmx write property regenMode
to allow (or not allow) regeneration. The NI-DAQmx default is to allow
regeneration.
•
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.
•
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. Use the
NI-DAQmx DO channel property, UseOnlyOnBoardMemeory to enable or
disable FIFO regeneration.
Digital Output Triggering
Digital output supports two different triggering actions:
•
Start trigger
•
Pause trigger
A digital trigger can initiate these actions. Refer to the
and
sections for more information about these triggering actions.
Digital Waveform Generation
Digital waveforms can be generated on the Port 0 DIO lines. The DO waveform generation FIFO
stores the digital samples. NI 6614 has a DMA controller dedicated to moving data from the
system memory to the DO waveform generation FIFO. The device moves samples from the
FIFO to the DIO terminals on each rising- or falling-edge of a clock signal, DO Sample Clock.
Each DIO signal is configurable to be an input, a static output, or a digital waveform generation
output.
The FIFO supports a retransmit mode. In the retransmit mode, after all the samples in the FIFO
have been clocked out, the FIFO begins outputting all of the samples again in the same order.
