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Chapter 7
PFI
Connecting PFI Input Signals
PFI Filters
NI-DAQmx only supports filters on counter inputs.
Note
NI USB-621x User Manual
All PFI input connections are referenced to D GND. Figure 7-3 shows this
reference, and how to connect an external PFI 0 source and an external
PFI 2 source to two PFI terminals.
PFI 0
Source
Figure 7-3. PFI Input Signals Connections
You can enable a programmable debouncing filter on each PFI signal.
When the filters are enabled, your device samples the input on each rising
edge of a filter clock. USB-621x devices use an onboard oscillator to
generate the filter clock with a 40 MHz frequency.
The following is an example of low to high transitions of the input signal.
High to low transitions work similarly.
PFI 2
Source
I/O Connector
7-4
PFI 0
PFI 2
D GND
USB-621x Device
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