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Chapter 4 Analog Input

AI Hold Complete Event Signal

The AI Hold Complete Event (ai/HoldCompleteEvent) signal generates a

pulse after each A/D conversion begins. You can route

ai/HoldCompleteEvent out to any PFI <4..8> or PFI <12..15> terminal.

The polarity of ai/HoldCompleteEvent is software-selectable, but is

typically configured so that a low-to-high leading edge can clock external

AI multiplexers indicating when the input signal has been sampled and can

be removed.

AI Start Trigger Signal

Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement

acquisition. A measurement acquisition consists of one or more samples. If

you do not use triggers, begin a measurement with a software command.

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.

Using a Digital Source

To use ai/StartTrigger with a digital source, specify a source and an edge.

The source can be any of the following signals:

• PFI <0..3>, PFI <8..11>

• Counter n Internal Output

The source also can be one of several other internal signals on your DAQ

device. Refer to Device Routing in MAX in the NI-DAQmx Help or the

LabVIEW 8.x Help for more information.

You also can specify whether the measurement acquisition begins on the

rising edge or falling edge of ai/StartTrigger.

Routing AI Start Trigger to an Output Terminal

You can route ai/StartTrigger out to any PFI <4..8> or PFII <12..15>

terminal.

The output is an active high pulse.

National Instruments NI USB-621x User Manual

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