Chapter 6
Digital I/O
X Series User Manual
6-26
ni.com
The filter setting for each inp
u
t can be config
u
red independently. On power
u
p, the filters are disabled. Fig
u
re 6-12 shows an example of a low-to-high
transition on an inp
u
t.
Figure 6-12.
Input Low-to-High Transition
When m
u
ltiple lines are config
u
red with the same filter settings they are
considered a b
u
s. There are two filtering modes for
u
se with m
u
ltiple lines:
line filtering and b
u
s filtering. With line filtering, each line transitions
independently of the other lines in the b
u
s and acts like the behavior
described above. With b
u
s filtering, if any one line in the b
u
s has jitter then
all lines in the b
u
s will hold state
u
ntil the b
u
s becomes stable. However,
each individ
u
al line will only wait one extra filter tick before changing.
This prevents a noisy line from holding a valid transition indefinitely. With
b
u
s mode if all the b
u
s line transitions become stable in less than one filter
clock period and the b
u
s period is more than two filter clock periods, then
all the b
u
s lines are g
u
aranteed to be correlated at the o
u
tp
u
t of the filter, as
shown in the fig
u
re.
Table 6-1.
Filters
Filter Setting
Filter Clock
Pulse Width Guaranteed
to Pass Filter
Pulse Width Guaranteed
to Not Pass Filter
Short
12.5 MHz
160 ns
80 ns
Medi
u
m
195.3125 kHz
10.24
μ
s
5.12
μ
s
High
390.625 Hz
5.12 ms
2.56 ms
None
—
—
—
Digit
a
l Inp
u
t P0.
x
Filter Clock
Filtered Inp
u
t
1
1
2
1
1
2
1
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