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Chapter 6
Digital I/O
©
National Instruments
6-25
X Series User Manual
The Change Detection Event signal can do the following:
•
Drive any RTSI <0..7>, PFI <0..15>, or PXI_STAR signal
•
Drive the DO Sample Clock or DI Sample Clock
•
Generate an interr
u
pt
The Change Detection Event signal also can be
u
sed to detect changes on
digital o
u
tp
u
t events.
DI Change Detection Applications
The DIO change detection circ
u
itry can interr
u
pt a
u
ser program when
one of several DIO signals changes state.
Yo
u
also can
u
se the o
u
tp
u
t of the DIO change detection circ
u
itry to trigger
a DI or co
u
nter acq
u
isition on the logical OR of several digital signals. To
trigger on a single digital signal, refer to the
Triggering with a Digital
Source
section of Chapter 11,
Triggering
. By ro
u
ting the Change Detection
Event signal to a co
u
nter, yo
u
also can capt
u
re the relative time between b
u
s
changes.
Yo
u
also can
u
se the Change Detection Event signal to trigger DO or
co
u
nter generations.
Digital Filtering
Yo
u
can enable a programmable debo
u
ncing filter on each digital line on
Port 0. When the filters are enabled, yo
u
r device samples the inp
u
t on each
rising edge of a filter clock. X Series devices divide down the onboard
100 MHz or 100 kHz clocks to generate the filter clock. The following is
an example of low-to-high transitions of the inp
u
t signal. High-to-low
transitions work similarly.
Ass
u
me that an inp
u
t terminal has been low for a long time. The inp
u
t
terminal then changes from low-to-high, b
u
t glitches several times. When
the filter clock has sampled the signal high on two consec
u
tive edges and
the signal remained stable in between, the low-to-high transition is
propagated to the rest of the circ
u
it.
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