38.14.1 Zero Crossing Detection
A zero-crossing is a point where the sign of a signal’s mathematical function changes
(e.g. from positive to negative), represented by a crossing of the axis (zero value) in the
graph of the signal function. It is a commonly used in electronics application especially
for systems which send digital data over AC circuits.
When in some cases, the “Zero point” could be other voltage than actual 0 V. This “Zero
point” would be used to judge whether the indicated voltage level is reached. In this
situation, the internal DAC could generate the reference voltage level for “Zero point” to
make the comparison with the other input channel of CMP module, and then output the
result of logic “0” and “1”.
To enable the internal DAC and set it as the comparator’s input of minus side, the code
could be as follow:
/* Set internal DAC as minus input. */
CMPx_C1 &= ~CMP_C1_ INNSEL_MASK;
/* Set input channel 3 as plus input. */
CMPx_C1 = (CMPx_C1 & ~(CMP_C1_ INPSEL_MASK | CMP_C1_PSEL_MASK))
| CMP_C1_INPSEL(1) | CMP_C1_PSEL(3);
Then, the CMP output interrupts with their flags would be used to indicate the event of
Zero Crossing Detection.
Chapter 38 Comparator (CMP)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors
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