National Instruments NI 6612, Руководство пользователя

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Chapter 2 Digital I/O
• With FIFO 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 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 after the operation is started, thereby
preventing any problems that may occur due to excessive bus traffic. Use the
NI-DAQmx DO channel property, UseOnlyOnBoardMemory 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 DO Start Trigger Signal and DO Pause
Trigger Signal 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 6612 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.
For example, if the FIFO contains five samples, the pattern generated consists of sample #1, #2,
#3, #4, #5, #1, #2, #3, #4, #5, #1, and so on.
The following DO (waveform generation) timing signals are featured:
• DO Sample Clock Signal *
• DO Sample Clock Timebase Signal
• DO Start Trigger Signal *
• DO Pause Trigger Signal *
Signals with an * support digital filtering. Refer to the PFI Filters section of Chapter 4, PFI , for
more information.