NXP Semiconductors Kinetis KE1xZ256, Reference Manual

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Table 37-6. CMP channel decoding in functional mode and trigger mode (continued)
Mode RRE PSEL[
2:0]
MSEL[
2:0]
INPSE
L[1:0]
INNSE
L[1:0]
FXMP FXMX
CH[2:0
]
CHNx INP INN CMP
Behavior
x x 1 1 0 0~7 0~7 Channel
fixed by
FXMXCH[
2:0] Channel
sweep
(CHN
x )
Channel 0~7
can be swept
with a fixed
channel
(0~7)
3
x x 1 1 1 0~7 0~7 Channel
sweep
(CHN
x )
Channel
fixed by
FXMXCH[
2:0] Channel 0~7
can be swept
with a fixed
channel
(0~7)
3
1. "x" means "do not care".
2. PSEL should not be set the same as MSEL.
3. Channel in the sweep side should not be the same as the fixed side.
37.14 Usage Guide
37.14.1 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.
Usage Guide
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
816 NXP Semiconductors