National Instruments Eight-slot USB Chassis NI cDAQ-9172 - Manual (Page 69)

© National Instruments Corporation 69 NI cDAQ-9172 User Guide and Specifications
Other Counter Features
Cascading Counters
You can internally route the Counter n Internal Output and Counter n TC
signals of each counter to the Gate inputs of the other counter. By cascading
two counters together, you can effectively create a 64-bit counter. By
cascading counters, you also can enable other applications. For example,
to improve the accuracy of frequency measurements, use reciprocal
frequency measurement, as described in the
Method 3—Measure Large
Range of Frequencies Using Two Counters section.
Counter Filters
You can enable a programmable debouncing filter on each PFI signal.
When the filters are enabled, the NI cDAQ-9172 chassis samples the input
on each rising edge of a filter clock. The NI cDAQ-9172 chassis uses an
onboard oscillator to generate the filter clock with a 40 MHz frequency.
For more information, refer to the NI-DAQmx Help. The NI-DAQmx Help
is available after installation from Start»All Programs»National
Instruments»NI-DAQ»NI-DAQmx Help.
Note NI-DAQmx only supports filters on counter inputs.
The following is an example of low to high transitions of the input signal.
High to low transitions work similarly.
Assume that an input terminal has been low for a long time. The input
terminal then changes from low to high, but glitches several times. When
the filter clock samples the signal high on N consecutive edges, the low to
high transition is propagated to the rest of the circuit. The value of N
depends on the filter setting, as listed in Table 9.
Table 9. Counter Input Filters
Filter Setting
N (Filter Clocks
Needed to
Pass Signal)
Pulse Width
Guaranteed to
Pass Filter
Pulse Width
Guaranteed to
Not Pass Filter
125 ns 5 125 ns 100 ns
6.425 µs 257 6.425 µs 6.400 µs
2.56 ms ~101,800 2.56 ms 2.54 ms
Disabled — — —