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example, four. The value decrements with each pulse on ai/SampleClock,
until the value reaches zero. The sample counter is then loaded with the
number of posttriggered samples, in this example, three.
ai/ReferenceTrigger
If an ai/ReferenceTrigger pulse occurs before the specified number of
pretrigger samples are acquired, the trigger pulse is ignored. Otherwise,
when the ai/ReferenceTrigger pulse occurs, the sample counter value
decrements until the specified number of posttrigger samples have been
acquired.
NI 6238/6239 devices feature the following analog input timing signals.
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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/SampleClock. A measurement
acquisition consists of one or more samples.
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ai/StartTrigger
n/a
ai/SampleClock
ai/ConvertClock
Scan Counter
3
2
Figure 4-10. Pretriggered Data Acquisition Example
AI Sample Clock Signal
AI Sample Clock Timebase Signal
AI Convert Clock Signal
AI Convert Clock Timebase Signal
AI Hold Complete Event Signal
AI Start Trigger Signal
AI Reference Trigger Signal
AI Pause Trigger Signal
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Chapter 4
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NI 6238/6239 User Manual
Analog Input
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