National Instruments NI 6014 - Manual (Page 60)

Chapter 4 Connecting Signals
NI 6013/6014 User Manual 4-34 ni.com
The maximum allowed frequency is 20 MHz, with a minimum pulse width
of 23 ns high or low. There is no minimum frequency limitation.
Either the 20 MHz or 100 kHz internal timebase normally generates
UISOURCE unless you select some external source.
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, GPCTR0_SOURCE 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, GPCTR0_SOURCE reflects the actual clock connected to
general-purpose counter 0, even if another PFI externally inputs the source
clock. This output is set to high-impedance at startup.
Figure 4-29 shows the timing requirements for GPCTR0_SOURCE.
Figure 4-29. 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 GPCTR0_SOURCE
unless you select some external source.
t
w
= 23 ns minimum
t
p
= 50 ns minimum
t
w
t
w
t
p