Chapter 4
Connecting the Signals
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National Instruments Corporation
4-39
GPCTR0_SOURCE Signal
Any PFI pin can externally input the GPCTR0_SOURCE signal, which
is available as an output on the PFI8/GPCTR0_SOURCE pin.
As an input, the GPCTR0_SOURCE signal is configured in the
edge-detection mode. You can select any PFI pin as the source for
GPCTR0_SOURCE and configure the polarity selection for either rising
or falling edge.
As an output, GPCTR0_SOURCE reflects the actual clock connected to
general-purpose counter 0, even if another PFI externally inputs the source
clock. This output is set to high-impedance at startup.
The maximum allowed frequency is 20 MHz, with a minimum pulse width
of 23 ns high or low. There is no minimum frequency.
The 20 MHz or 100 kHz timebase normally generates GPCTR0_SOURCE
unless you select some external source.
Figure 4-33 shows the timing requirements for GPCTR0_SOURCE.
Figure 4-33.
GPCTR0_SOURCE Signal Timing
GPCTR0_GATE Signal
Any PFI pin can externally input GPCTR0_GATE, which is available as an
output on the PFI9/GPCTR0_GATE pin.
As an input, GPCTR0_GATE is configured in the edge-detection mode.
You can select any PFI pin as the source for GPCTR0_GATE and configure
the polarity selection for either rising or falling edge. You can use the gate
signal in different applications to perform actions such as starting and
stopping the counter, generating interrupts, and saving the counter contents.
t
w
= 23 ns minimum
t
p
= 50 ns minimum
t
w
t
w
t
p
