Gpctr1_Source Signal; Gpctr1_Gate Signal; Figure 4-11. Gpctr1_Source Signal Timing - National Instruments DAQ PCI-4451 User Manual

Chapter 4 Signal Connections

GPCTR1_SOURCE Signal

Any PFI pin can externally input the GPCTR1_SOURCE signal, which is
available as an output on the PFI3/GPCTR1_SOURCE pin.
As an input, the GPCTR1_SOURCE signal is configured in edge-detection
mode. You can select any PFI pin as the source for GPCTR1_SOURCE and
configure the polarity selection for either rising or falling edge.
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 tri-state at
startup.
Figure 4-11 shows the timing requirements for the GPCTR1_SOURCE
signal.
t
p
t t
w w
t
= 50 ns minimum
p
t
= 23 ns minimum
w

Figure 4-11. 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

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, 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.
© National Instruments Corporation 4-21 PCI-4451/4452 User Manual