Chapter 4
Analog Input
4-14
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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
section.
In order to provide all of the timing functionality described throughout this
section, the DAQ-STC2 provides an extremely powerful and flexible
timing engine. For more information about all of the clock routing and
timing options that the analog input timing engine provides, refer to the
NI-DAQmx Help
or the
LabVIEW Help
in version 8.0 or later.
S Series devices feature the following analog input timing signals:
•
AI Sample Clock Signal
•
AI Sample Clock Timebase Signal
•
•
AI Convert Clock Timebase Signal
•
•
•
AI Sample Clock Signal
Use the AI Sample Clock (ai/SampleClock) signal to initiate a set of
measurements. Your S Series device samples the AI signals of every
channel in the task once for every AI Sample Clock.
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.
Using an Internal Source
One of the following internal signals can drive AI Sample Clock:
•
Counter
n
Internal Output
•
AI Sample Clock Timebase (divided down)
•
A pulse initiated by host software
A programmable internal counter divides down the sample clock timebase.
