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Chapter 2
Using the NI PXIe-4300
Figure 2-6 shows the relationship of AI Sample Clock to AI Start Trigger.
AI Sample Clock Timebase Signal
You can route any of the following signals to be the AI Sample Clock Timebase
(ai/SampleClockTimebase) signal:
•
100 MHz Timebase (default)
•
20 MHz Timebase
•
100 kHz Timebase
•
PXI_CLK10
•
PXI_Trig <0..7>
•
PFI <0,1>
•
PXI_STAR
•
PXIe_DSTAR <A, B>
AI Sample Clock Timebase is not available as an output on the I/O connector. AI Sample Clock
Timebase is divided down to provide one of the possible sources for AI Sample Clock. You can
configure the polarity selection for AI Sample Clock Timebase as either rising or falling edge,
except on 100 MHz Timebase or 20 MHz Timebase.
AI Start Trigger Signal
Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement acquisition. A
measurement acquisition consists of one or more samples. If you do not use triggers, begin a
measurement with a software command by starting a task, which sends the software command
that begins the measurement. Once the acquisition begins, configure the acquisition to stop:
•
When a certain number of points are sampled (in finite mode)
•
After a hardware reference trigger (in finite mode)
•
With a software command (in continuous mode)
An acquisition that uses a start trigger (but not a reference trigger) is sometimes referred to as a
posttriggered acquisition.
2-12 | ni.com
Figure 2-6. AI Sample Clock and AI Start Trigger
AI Sample Clock Timebase
AI Start Trigger
AI Sample Clock
Delay
From
Start
Trigger
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