Keithley KPCI-3101 Series, User Manual

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2-12 Principles of Operation KPCI-3101 — KPCI-3104 Series User’s Manual
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, acquisition stops. Refer to
page 2-8 for more informa-
tion on internally-retriggered scan mode.
Figure 2-4 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. When it reaches the end of the channel-gain list, the
board wraps to the beginning of the channel-gain list and repeats this process. Data is acquired
continuously until the post-trigger event occurs. When the post-trigger event occurs, acquisition
stops.
Figure 2-4
Continuous pre-trigger mode
Figure 2-5 illustrates the same example using internally-retriggered scan mode. The multiscan
count is 2, indicating that the channel-gain 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-gain list has been scanned twice; then, the board waits for the internal
retrigger event. When the internal retrigger occurs, the process repeats. Acquisition stops when
the post-trigger event occurs.
Figure 2-5
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 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.