General-Purpose Timing Signal Connections; Gpctr0_Source Signal; Figure 4-9. Gpctr0_Source Signal Timing - National Instruments DAQ PCI-4451 User Manual

General-Purpose Timing Signal Connections

© National Instruments Corporation
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.
t
w

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
= 50 ns minimum
p
t
= 23 ns minimum
w
4-19
Chapter 4 Signal Connections
PCI-4451/4452 User Manual