Chapter 4

Analog Input

ai/StartTrigger

ai/ReferenceTrigger n/a

ai/SampleClock

ai/ConvertClock

Scan Counter

3

2

1

0

2

2

2

1

0

Figure 4-7.Pretriggered Data Acquisition Example

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.

USB M Series devices feature the following analog input timing signals.

•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

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.

You can specify an internal or external source for ai/SampleClock. You also can specify whether the measurement sample begins on the rising edge or falling edge of ai/SampleClock.