Measurement Computing Data Translation DT3034, User Manual

Page: 84 / 178

Principles of Operation
83
If you are using software-retriggered scan mode and the post-trigger event has not occurred,
the board continues to acquire pre-trigger data using the Triggered Scan Counter to clock the
operation. When the post-trigger event occurs, the operation stops. Refer to
page 77 for more
information on software-retriggered scan mode.
Figure 24 illustrates continuous pre-trigger mode using a channel list of three entries: channel
0, channel 1, and channel 2. In this example, pre-trigger analog input data is acquired on each
clock pulse of the A/D sample clock. The board wraps to the beginning of the channel list and
the acquisition repeats continuously until the post-trigger event occurs. When the post-trigger
event occurs, acquisition stops.
Figure 24: Continuous Pre-Trigger Mode
Figure 25 illustrates the same example using software-retriggered triggered scan mode. The
multiscan count is 2 indicating that the channel list will be scanned twice per trigger or
retrigger. In this example, pre-trigger analog input data is acquired on each clock pulse of the
A/D sample clock until the channel list has been scanned twice; then, the board waits for the
software retrigger event. When the software retrigger occurs, the process repeats. The process
stops when the post-trigger event occurs.
Figure 25: Continuous Pre-Trigger Mode with Triggered Scan
Pre-trigger event occurs
Chan 0
Chan 1
Chan 2 Chan 0
Chan 1
Chan 2
A/D
Sample
Clock
Post-trigger event occurs
Chan 0
Pre-trigger data acquired
Acquisition stops
Pre-trigger event occurs;
pre-trigger data is
acquired for two scans of
the channel list.
Chan 0
Chan 1
Chan 2 Chan 0
Chan 1
Chan 2
A/D
Sample
Clock
Chan 0
Chan 1
Chan 2 Chan 0
Retrigger event occurs;
pre-trigger data is
acquired until
post-trigger event
occurs.
Board waits for
retrigger event.
Post-trigger even
occurs; acquisitio
stops.