Chapter 4
Connecting Signals
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National Instruments Corporation
4-37
Figure 4-32 shows the timing requirements for GPCTR1_SOURCE.
Figure 4-32.
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 GPCTR1_SOURCE
unless you select some external source.
GPCTR1_GATE Signal
Any PFI pin can externally input the GPCTR1_GATE signal, which
is available as an output on the PFI4/GPCTR1_GATE pin.
As an input, GPCTR1_GATE 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, GPCTR1_GATE monitors the actual gate signal connected
to general-purpose counter 1, even if the gate is being externally generated
by another PFI. This output is set to high-impedance at startup.
t
w
= 23 ns minimum
t
p
= 50 ns minimum
t
w
t
w
t
p
