Chapter 7 Counters
X Series User Manual 7-2 ni.com
generations. The embedded counters cannot be programmed independent
of the main counter; signals from the embedded counters are not routable.
Counter Timing Engine
Unlike analog input, analog output, digital input, and digital output,
X Series 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 <0..15>
• PXI_Trig <0..7>
• 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 measu rement, 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.
Table 7-1 shows the different options for the different measurements.
Note All hardware-timed single point (HWTSP) operations are sample clocked.
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