© National Instruments
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4-23
M Series User Manual
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 pretriggered 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 posttriggered samples, in this example, three.
Figure 4-15.
Pretriggered Data Acquisition Example
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.
M Series devices feature the following analog input timing signals:
•
AI Sample Clock Signal
•
AI Sample Clock Timebase Signal
•
AI Convert Clock Signal
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AI Convert Clock Timebase Signal
•
AI Hold Complete Event Signal
•
AI Start Trigger Signal
•
AI Reference Trigger Signal
•
AI Pause Trigger Signal
AI Sample Clock Signal
Use the AI Sample Clock (ai/SampleClock) signal to initiate a set of measurements. Your
M Series device samples the AI signals of every channel in the task once for every AI Sample
Clock. A measurement acquisition consists of one or more samples.
You can specify an internal or external source for AI Sample Clock. You also can specify
whether the measurement sample begins on the rising edge or falling edge of AI Sample Clock.
n/a
0
1
2
3
1
0
2
2
2
AI Start Trigger
AI Reference Trigger
AI Sample Clock
AI Convert Clock
Scan Counter
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