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Chapter 3 Connecting the Signals
DAQCard-1200 User Manual 3-24 ni.com
Figure 3-14. Posttrigger DAQ Timing
In the pretrigger mode, EXTTRIG serves as a stop-trigger signal. Data is
acquired both before and after the stop trigger occurs. A/D conversions are
software enabled, which initiates the DAQ operation. However, the sample
counter is not started until a rising edge is sensed on the EXTTRIG input.
Conversions remain enabled until the sample counter counts to zero. The
maximum number of samples acquired after the stop trigger is limited to
65,535. The number of samples acquired before the trigger is limited only
by the size of the memory buffer available for data acquisition.
Figure 3-15 shows a pretrigger DAQ timing sequence using EXTTRIG and
EXTCONV*. The DAQ operation has been initiated through software.
Notice that the sample counter has been programmed to allow five
conversions after the rising edge on the EXTTRIG signal. Additional
transitions on the EXTTRIG line have no effect until you initiate a new
DAQ sequence.
CONVERT
EXTCONV*
EXTTRIG
V
IH
V
IL
t
w
t
w
t
d
t
w
50 ns minimum
t
d
50 ns minimum
First posttrigger sample