Keithley KPCI-3110, User Manual

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2-12 Functional Description KPCI-3110 and KPCI-3116 User’s Manual
Figure 2-4 illustrates the same example using triggered scan mode (either internally- or exter-
nally-retriggered). The multiscan count is 2 indicating that the channel-gain 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-gain list has been scanned twice; then, the
board waits for the retrigger event. When the retrigger event occurs, the board scans the channel-
gain list twice more, acquiring data on each pulse of the A/D sample clock. The process repeats
continuously with every specified retrigger event.
Figure 2-4
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 following parameters:
• The dataflow as continuous pre-trigger
•
The pre-trigger source as the software trigger
• The post-trigger source as the external digital (TTL) trigger or the external analog threshold
trigger
•
If you are using triggered scan mode, the retrigger mode as the internal retrigger
Refer to page 2-7 for more information on the supported conversion modes. Refer to page 2-10
for information on the supported trigger sources.
When using pre-trigger acquisition, you cannot use an external retrigger in triggered scan mode.
Refer to
page 2-8 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 sam-
ple is ignored).
If you are using internally-retriggered scan mode and the post-trigger event has not occurred, the
board continues to acquire pre-trigger data using the internal retrigger clock to clock the opera-
tion. When the post-trigger event occurs, the operation stops. Refer to
page 2-8 for more infor-
mation on internally-retriggered scan mode.
Figure 2-5 illustrates continuous pre-trigger mode using a channel-gain 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-gain
list and the acquisition repeats continuously until the post-trigger event occurs. When the post-
trigger event occurs, acquisition stops.
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
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.