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Chapter 4 Connecting Signals
© National Instruments Corporation 4-23 NI 6115/6120 User Manual
selection for either rising or falling edge. The selected edge of TRIG2
initiates the posttriggered phase of a pretriggered DAQ sequence. In
pretriggered mode, the TRIG1 signal initiates the acquisition. The scan
counter indicates the minimum number of scans before TRIG2 can be
recognized. After the scan counter decrements to zero, it is loaded with the
number of posttrigger scans to acquire while the acquisition continues.
The device ignores TRIG2 if it is asserted prior to the scan counter
decrementing to zero. After the selected edge of TRIG2 is received, the
device acquires a fixed number of scans and the acquisition stops. This
mode acquires data both before and after receiving TRIG2.
As an output, TRIG2 reflects the posttrigger in a pretriggered DAQ
sequence even if another PFI is externally triggering the acquisition.
TRIG2 is not used in posttriggered data acquisition. The output is an active
high pulse with a pulse width of 25 to 50 ns. This output is set to
high-impedance at startup.
Figures 4-16 and 4-17 show the timing requirements for TRIG2.
Figure 4-16. TRIG2 Input Signal Timing
Figure 4-17. TRIG2 Output Signal Timing
Rising-Edge
Polarity
Falling-Edge
Polarity
t
w
= 10 ns minimum
t
w
t
w
t
w
= 25 – 50 ns