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You might use the AI Sample Clock Timebase if you want to use an external clock signal, but
need to divide the signal down. If you want to use an external sample clock signal, but do not
need to divide the signal, you should use AI Sample Clock rather than AI Sample Clock
Timebase.
You might also use the AI Sample Clock Timebase if you want to synchronize multiple
measurement devices by locking to a shared clock. For more information, refer to the
Synchronizing Multiple Devices
section
.
You can configure the polarity selection for AI Sample Clock Timebase as either rising or falling
edge, except on 100 MHz Timebase or 20 MHz Timebase.
AI Start Trigger Signal
You can use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement acquisition. If
you do not use triggers, begin a measurement with a software command by starting a task, which
creates a software generated pulse to start the acquisition. Once the acquisition begins, configure
the acquisition to stop:
•
When a certain number of points are sampled (in finite mode)
•
After a hardware reference trigger (in finite mode)
•
With a software command (in continuous mode)
An acquisition that uses a start trigger (but not a reference trigger) is sometimes referred to
as a posttriggered acquisition. 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 3-2. 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 3-2.
Typical Posttriggered DAQ Sequence
Your DAQ device only acquires data after a start trigger pulse. The device ignores AI Sample
Clock if a start trigger pulse has not occurred.
1
3
0
4
2
AI Start Trigger
AI Sample Clock
Sample Counter
