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Chapter 7
PFI
7-4
ni.com
Connecting PFI Input Signals
All PFI inp
u
t connections are referenced to D GND. Fig
u
reference, and how to connect an external PFI 0 so
u
rce and an external
PFI 2 so
u
rce to two PFI terminals.
Figure 7-3.
PFI Input Signals Connections
PFI Filters
Yo
u
can enable a programmable debo
u
ncing filter on each PFI signal.
When the filters are enabled, yo
u
r device samples the inp
u
t on each rising
edge of a filter clock. USB-621
x
devices
u
se an onboard oscillator to
generate the filter clock with a 40 MHz freq
u
ency.
Note
NI-DAQmx
only
s
u
pports filters on co
u
nter inp
u
ts.
The following is an example of low to high transitions of the inp
u
t signal.
High to low transitions work similarly.
PFI 0
S
o
u
rce
PFI 2
S
o
u
rce
U
S
B-621
x
Device
D GND
PFI 2
PFI 0
I/O Connector