Data Translation DT300 Series, Руководство пользователя, Страница: 82 / 164

Chapter 6
82
Figure 26 illustrates the same example using triggered scan mode (either internally or
externally retriggered). The multiscan count is 2, indicating that the channel list will be
scanned twice per trigger or retrigger. In this example, post-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 retrigger event. When the retrigger event occurs, the board
scans the channel list twice more, acquiring data on each pulse of the A/D sample clock. The
process repeats continuously with every specified retrigger event.
Figure 26: Continuous Post-Trigger Mode with Triggered Scan
Pre-Trigger Acquisition
Use pre-trigger acquisition mode (continuous pre-trigger mode) when you want to acquire
data before a specific external event occurs.
Using software, specify:
• The dataflow as ContinuousPreTrigger
• The pre-trigger source as the software trigger
• The post-trigger source as the external, positive, digital (TTL) trigger
• The retrigger mode as the software retrigger if you are using triggered scan mode
Refer to page 77 for more information on the supported conversion modes; refer to page 80 for
information on the supported trigger sources.
Note: When using pre-trigger acquisition, you cannot use externally-retriggered scan mode;
refer to page 78 for more information on triggered scan mode.
Pre-trigger acquisition starts when you start the operation and stops when the board detects
the selected post-trigger source, indicating that the first post-trigger sample was acquired (this
sample is ignored).
Post-trigger event occurs;
post-trigger data 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
Chan 1
Chan 2
Retrigger event occurs;
post-trigger data acquired
for two scans of the CGL.
Board waits for
retrigger event.