Chapter 3
Connecting the Signals
©
National Instruments Corporation
3-37
DAQPad-MIO-16XE-50 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 signal can externally input GPCTR0_SOURCE, which is
available as an output on the PFI8/GPCTR0_SOURCE screw terminal.
As an input, the GPCTR0_SOURCE signal is configured in the
edge-detection mode. You can select any PFI signal 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, even if another PFI is externally
inputting the source clock. This output is set to high-impedance at start up.
Figure 3-28 shows the timing requirements for the GPCTR0_SOURCE
signal.
Figure 3-28.
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
w
= 23 ns minimum
t
p
= 50 ns minimum
t
w
t
w
t
p
