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Chapter 4
Digital Input/Output and PFI
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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.
Note
Install parallel DO modules in slots 1 through 4 to maximize accessible FIFO
size because using a module in slots 5 through 8 will reduce the accessible FIFO size.
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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.
Digital Output Triggering Signals
Digital output supports two different triggering actions: DO Start Trigger and DO Pause Trigger.
A digital or analog trigger can initiate these actions. Any PFI terminal can supply a digital
trigger, and some C Series analog modules can supply an analog trigger. For more information,
refer to the documentation included with your C Series module(s).
Refer to the
sections for more
information about the digital output trigger signals.
Digital Output Timing Signals
The cDAQ chassis features the following DO timing signals:
•
•
DO Sample Clock Timebase Signal
•
•
Signals with an * support digital filtering. Refer to the
section for more information.
