Chapter 9 | Counters |
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Signal of Known | SOURCE | OUT | |
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0 1 2 3 … N
CTR_0_SOURCE (Signal to Measure)
CTR_0_OUT
(CTR_1_GATE) Interval to Measure
CTR_1_SOURCE
Figure
Then route the Counter 0 Internal Output signal to the Gate input of Counter 1. You can route a signal of known frequency (F2) to the Counter 1 Source input. F2 can be 80MHzTimebase. For signals that might be slower than 0.02 Hz, use a slower known timebase. Configure Counter 1 to perform a single
From Counter 0, the length of the pulse is N/F1. From Counter 1, the length of the same pulse is J/F2. Therefore, the frequency of F1 is given by
F1 = F2 * (N/J).
Choosing a Method for Measuring Frequency
The best method to measure frequency depends on several factors including the expected frequency of the signal to measures, the desired accuracy, how many counters are available, and how long the measurement can take.
•Method 1 uses only one counter. It is a good method for many applications. However, the accuracy of the measurement decreases as the frequency increases.
Consider a frequency measurement on a 50 kHz signal using an
80 MHz Timebase. This frequency corresponds to 1600 cycles of the
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