Data Translation DT300 Series, Руководство пользователя, Страница: 83 / 164

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 software retrigger clock to clock the
operation. When the post-trigger event occurs, acquisition stops. Refer to
page 78 for more
information on software-retriggered scan mode.
Figure 27 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. When it reaches the end of the channel list, the board
wraps to the beginning of the channel list and repeats this process. Data is acquired
continuously until the post-trigger event occurs. When the post-trigger event occurs,
acquisition stops.
Figure 27: Continuous Pre-Trigger Mode
Figure 28 illustrates the same example using software-retriggered 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. Acquisition stops
when the post-trigger event occurs.
Figure 28: 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
Chan 0
Pre-trigger data acquired
Acquisition stops
Pre-trigger event occurs;
pre-trigger data is acquired
for two scans of the CGL.
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 event
occurs; acquisition
stops.