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Chapter 2
NI 651x Features
The filter clock is programmable and allows you to control how long a pulse must last to be
recognized. The sample clock provides a fast sample rate to ensure that input pulses remain
constant between filter clocks.
Digital Filtering Example
Figure 2-1 shows a filter configuration with a t
interval
filter interval (t
interval
/2 filter clock).
Figure 2-1.
Digital Filtering Example
In periods A and B, the filter blocks the glitches because the external signal does not remain
steadily high from one rising edge of the filter clock to the next. In period C, the filter passes the
transition because the external signal remains steadily high. Depending on when the transition
occurs, the filter may require up to two filter clocks—one full filter interval—to pass a transition.
Figure 2-1 shows a rising (0 to 1) transition. The same filtering applies to falling (1 to 0)
transitions.
Note
NI 6512/6513/6516/6517 devices do not support digital filtering.
Programmable Power-Up States
At power-up, the output drives on the NI 651
x
device is disabled. All output lines are
user-configurable for an on or off state. User-configurable power-up states are useful for
ensuring that the NI 651
x
device powers up in a known state.
To use MAX (recommended) to program the power-up states, select the device and click the
Properties
button. Refer to the software documentation for information about how to program
the power-up states using NI-DAQ with LabVIEW or other National Instruments application
development environments (ADEs).
Note
The response time of programmable power-up states is 400 ms.
Note
NI 6510/6511 devices do not support programmable power-up states.
Extern
a
l
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ign
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Extern
a
l
S
ign
a
l
Sa
mpled
Filter
Clock
Sa
mple Clock (100 n
s
)
Filtered
S
ign
a
l
H
H
H
H
H
H
L
L
H
H
H
L
L
H
H
A
B
C
