Chapter 4
Signal Connections
©
National Instruments Corporation
4-21
PCI-4451/4452/4453/4454 User Manual
PFI1/TRIG2 (PRETRIG) Signal
Any PFI pin can receive as an input the PFI1/TRIG2 (PRETRIG) signal,
which is available as an output on the PFI1/TRIG2 (PRETRIG) pin.
Refer to Figure 4-10 for the relationship of PFI1/TRIG2 to the acquisition
sequence.
As an input, the PFI1/TRIG2 signal is configured in edge-detection mode.
You can select any PFI pin as the source for PFI1/TRIG2 and configure the
polarity selection for either rising or falling edge. The selected edge of the
PFI1/TRIG2 signal initiates the posttriggered phase of a pretriggered
acquisition sequence. In pretriggered mode, the PFI0/TRIG1 signal
initiates the data acquisition. The scan counter indicates the minimum
number of scans before PFI1/TRIG2 is 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 the
PFI1/TRIG2 signal if it is asserted prior to the scan counter decrementing
to zero. After the selected edge of PFI1/TRIG2 is received, the device
acquires a fixed number of scans and the acquisition stops. After
PFI1/TRIG2 is received, any additional PFI1/TRIG2 signals are ignored
until the acquisition is restarted. This mode acquires data both before and
after receiving PFI1/TRIG2.
As an output, the PFI1/TRIG2 signal reflects the posttrigger in a
pretriggered acquisition sequence. This is true even if the acquisition is
externally triggered by another PFI signal. The PFI1/TRIG2 signal is not
used in posttriggered data acquisition. The output is an active high pulse
with a pulse width of 50 to 100 ns. This output is set to high-impedance at
startup.
CONVERT* Signal
The CONVERT* signal is only available as an output on the CONVERT*
pin. The CONVERT* signal reflects the end of delta-sigma conversion on
the ADC. The output is an active-low pulse with a pulse width of
70 to 100 ns. This output is set to high-impedance at startup.
EXTSTROBE* Signal (PCI-4451/4452 Only)
EXTSTROBE* is an output-only signal that generates either a single pulse
or a sequence of eight pulses in the hardware-strobe mode. An external
device can use this signal to latch signals or to trigger events. In
single-pulse mode, software controls the level of the EXTSTROBE*
signal. A 10
µ
s and a 1.2
µ
s clock is available for generating a sequence
