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Chapter 4 Signal Connections
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National Instruments Corporation 4-19 PCI-4451/4452 User Manual
General-Purpose Timing Signal Connections
The general-purpose timing signals are GPCTR0_SOURCE,
GPCTR0_GATE, GPCTR0_OUT, GPCTR0_UP_DOWN,
GPCTR1_SOURCE, GPCTR1_GATE, GPCTR1_OUT,
GPCTR1_UP_DOWN, and FREQ_OUT.
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, the GPCTR0_SOURCE signal reflects the actual clock
connected to general-purpose counter 0. This is true even if another PFI
signal is externally inputting the source clock. This output is set to tri-state
at startup.
Figure 4-9 shows the timing requirements for the GPCTR0_SOURCE
signal.
Figure 4-9.
GPCTR0_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
GPCTR0_SOURCE signal unless you select some external source.
t
p
t
w
t
w
t
p
t
w
= 50 ns minimum
= 23 ns minimum
User.book Page 19 Tuesday, April 14, 1998 10:20 AM