© National Instruments Corporation 33 NI cDAQ-9178/9174 User Guide and Specifications
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. Table 4 shows the different options for the different
measurements.
Counter Input Applications
The following sections list the various counter input applications available on the NI cDAQ-9178/9174:
• Counting Edges
• Pulse-Width Measurement
• Pulse Measurement
• Semi-Period Measurement
Table 4. Counter Timing Measurements
Measurement
Implicit
Timing Support
Sample Clocked
Timing Support
Buffered Edge Count No Yes
Buffered Pulse Width Yes Ye s
Buffered Pulse Yes Ye s
Buffered Semi-Period Yes No
Buffered Frequency Yes Ye s
Buffered Period Yes Ye s
Buffered Position No Yes
Buffered Two-Signal Edge Separation Yes Ye s
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