National Instruments AT E Series - Manual (Page 92)

Chapter 4 Connecting Signals
© National Instruments Corporation 4-45 AT E Series User Manual
As an output, the GPCTR0_SOURCE signal reflects the actual clock
connected to general-purpose counter 0, even if another PFI is externally
inputting the source clock. This output is set to high-impedance at startup.
Figure 4-31 shows the timing requirements for the GPCTR0_SOURCE
signal.
Figure 4-31. 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.
GPCTR0_GATE Signal
Any PFI pin can externally input the GPCTR0_GATE signal, which is
available as an output on the PFI9/GPCTR0_GATE pin.
As an input, the GPCTR0_GATE signal 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 a variety of different applications to perform actions such
as starting and stopping the counter, generating interrupts, saving the
counter contents, and so on.
As an output, the GPCTR0_GATE signal reflects the actual gate signal
connected to general-purpose counter 0, 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