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Chapter 5 Digital Input/Output and PFI
– 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.
– 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
A trigger is a signal that causes an action, such as starting or stopping the acquisition of data.
When you configure a trigger, you must decide how you want to produce the trigger and the
action you want the trigger to cause. The cDAQ chassis supports internal software triggering,
external digital triggering, analog triggering, and internal time triggering.
Digital output supports two different triggering actions: DO Start Trigger and DO Pause Trigger.
A digital or analog trigger can initiate these actions. Time can also initiate the Start Trigger. 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 DO Start Trigger Signal and DO Pause Trigger Signal 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 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 for more information.
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