National Instruments X Series User Manual page 89

Chapter 4 Analog Input
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 4-28. 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 all desired samples have been acquired.
AI Start Trigger
AI Sample Clock
Sample Counter
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 4-29 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.The sample counter is then loaded with
the number of posttrigger samples, in this example, three.
AI Start Trigger
AI Reference Trigger
AI Sample Clock
Sample Counter
If an AI Reference Trigger (ai/ReferenceTrigger) pulse occurs before the specified number of
pretrigger samples are acquired, the trigger pulse is ignored. Otherwise, when the AI Reference
Trigger pulse occurs, the sample counter value decrements until the specified number of
posttrigger samples have been acquired. For more information about start and reference triggers,
refer to the Analog Input Triggering
Simultaneous MIO X Series devices feature the following analog input timing signals:
• AI Sample Clock Signal
• AI Sample Clock Timebase Signal
• AI Hold Complete Event Signal
• AI Start Trigger Signal
4-46 | ni.com
Figure 4-28. Typical Posttriggered DAQ Sequence
Figure 4-29. Typical Pretriggered DAQ Sequence
Don't Care
3
section.
*
*
4 3 2
2 1 0 2
1 0
2 2 1 0