80 MHz Source Mode
In 80 MHz source mode, the controller synchronizes signals on the rising edge of the source,
and counts on the third rising edge of the source. Edges are pipelined so no counts are lost, as
shown in the figure below.
Figure 48. 80 MHz Source Mode
80 MHz Source
Synchronize Count
External or Internal Source Less than 20 MHz
With an external or internal source less than 20 MHz, the module generates a delayed Source
signal by delaying the Source signal by several nanoseconds. The controller synchronizes
signals on the rising edge of the delayed Source signal, and counts on the following rising
edge of the source, as shown in the figure below.
Figure 49. External or Internal Source Less than 20 MHz
Source
Delayed Source
Synchronize
Count
Counter Input Applications
The following sections list the various counter input applications available on the cRIO
controller:
• Counting Edges
• Pulse-Width Measurement
• Pulse Measurement
• Semi-Period Measurement
• Frequency Measurement
• Period Measurement
• Position Measurement
• Two-Signal Edge-Separation Measurement
Counting Edges
In edge counting applications, the counter counts edges on its Source after the counter is
armed. You can configure the counter to count rising or falling edges on its Source input. You
cRIO-904x User Manual | © National Instruments | 77
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