Counter Timing Engine
Unlike analog input, analog output, digital input, and digital output, the cRIO controller
counters do not have the ability to divide down a timebase to produce an internal counter
sample clock. For sample clocked operations, an external signal must be provided to supply a
clock source. The source can be any of the following signals:
•
AI Sample Clock
•
AI Start Trigger
•
AI Reference Trigger
•
AO Sample Clock
•
DI Sample Clock
•
DI Start Trigger
•
DO Sample Clock
•
CTR
n
Internal Output
•
Freq Out
•
PFI
•
Change Detection Event
•
Analog Comparison Event
Not all timed counter operations require a sample clock. For example, a simple buffered pulse
width measurement latches in data on each edge of a pulse. For this measurement, the
measured signal determines when data is latched in. These operations are referred to as
implicit timed operations. However, many of the same measurements can be clocked at an
interval with a sample clock. These are referred to as sample clocked operations. The
following table shows the different options for the different measurements.
Table 17. Counter Timing Measurements
Measurement
Implicit Timing Support Sample Clocked Timing
Support
Buffered Edge Count
No
Yes
Buffered Pulse Width
Yes
Yes
Buffered Pulse
Yes
Yes
Buffered Semi-Period
Yes
No
Buffered Frequency
Yes
Yes
Buffered Period
Yes
Yes
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NI cRIO-905x User Manual
