© National Instruments
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2-9
Figure 2-3.
NI PXIe-4300 PGIA
Analog Input Timing Signals
In order to provide all of the timing functionality described throughout this section,
NI PXIe-4300 modules have a flexible timing engine.
NI PXIe-4300 modules use AI Sample Clock (ai/SampleClock) to perform simultaneous
sampling on all active analog channels. Since there is one ADC per channel, AI Sample Clock
controls the sample period on all the channels in the task.
An acquisition with posttrigger data allows you to view data that is acquired after a trigger event
is received. A typical posttrigger DAQ sequence is shown in Figure 2-4. The sample counter is
loaded with the specified number of posttrigger samples, in this example, five. The value
decrements with each pulse on AI Sample Clock, until the value reaches zero and all desired
samples have been acquired.
Figure 2-4.
Typical Posttriggered DAQ Sequence
An acquisition with pretrigger data allows you to view data that is acquired before the trigger of
interest, in addition to data acquired after the trigger. Figure 2-5 shows a typical pretrigger DAQ
sequence. The AI Start Trigger signal (ai/StartTrigger) can be either a hardware or software
signal. If AI Start Trigger is set up to be a software start trigger, an output pulse appears on the
ai/StartTrigger line when the acquisition begins. When the AI Start Trigger pulse occurs, the
sample counter is loaded with the number of pretrigger samples, in this example, four. The value
decrements with each pulse on AI Sample Clock, until the value reaches zero. The sample
counter is then loaded with the number of posttrigger samples, in this example, three.
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V
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red
Volt
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1
3
0
4
2
AI Start Trigger
AI Sample Clock
Sample Counter
