Chapter 4
Signal Connections
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National Instruments Corporation
4-25
PCI-4451/4452/4453/4454 User Manual
As an output, the GPCTR1_SOURCE monitors the actual clock connected
to general-purpose counter 1. This is true even if the source clock is
externally generated by another PFI signal. This output is set to
high-impedance at startup.
Figure 4-14 shows the timing requirements for the GPCTR1_SOURCE
signal.
Figure 4-14.
GPCTR1_SOURCE Signal Timing
The maximum allowed frequency is 20 MHz, with a minimum pulse width
of 23 ns high or low. There is no minimum frequency limitation.
The 20 MHz or 100 kHz timebase normally generates the
GPCTR1_SOURCE unless you select some external source.
GPCTR1_GATE Signal (PCI-4451/4452 Only)
Any PFI pin can receive as an input the GPCTR1_GATE signal, which is
available as an output on the PFI4/GPCTR1_GATE pin.
As an input, the GPCTR1_GATE signal is configured in edge-detection
mode. You can select any PFI pin as the source for GPCTR1_GATE and
configure the polarity selection for either rising or falling edge. You can use
the GATE signal in a variety of different applications to perform such
actions as starting and stopping the counter, generating interrupts, saving
the counter contents, and so on.
As an output, the GPCTR1_GATE signal monitors the actual GATE signal
connected to general-purpose counter 1. This is true even if the GATE is
externally generated by another PFI signal. This output is set to
high-impedance at startup.
t
p
t
w
t
w
t
p
t
w
= 50 ns minimum
= 23 ns minimum
