K60P100M100SF2RM Datasheet, PDF (880/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

CMP Functional Description
If CR1[SE]=1, the filter takes samples of COUTA on each positive transition of the
sample input. The output state of the filter changes when CR0[FILTER_CNT]
consecutive samples all agree that the output value has changed.
35.8.4.2 Latency Issues
The FPR[FILT_PER] value (or SAMPLE period) should be set such that the sampling
period is just larger than the period of the expected noise. This way a noise spike will
only corrupt one sample. The CR0[FILTER_CNT] value should be chosen to reduce the
probability of noisy samples causing an incorrect transition to be recognized. The
probability of an incorrect transition is defined as the probability of an incorrect sample
raised to the CR0[FILTER_CNT] power.
The following table summarizes maximum latency values for the various modes of
operation in the absence of noise. Filtering latency is restarted each time an actual output
transition is masked by noise.
The values of FPR[FILT_PER] (or SAMPLE period) and CR0[FILTER_CNT] must also
be traded off against the desire for minimal latency in recognizing actual comparator
output transitions. The probability of detecting an actual output change within the
nominal latency is the probability of a correct sample raised to the CR0[FILTER_CNT]
power.
Table 35-30. Comparator Sample/Filter Maximum Latencies
Mode #
CR1[
EN]
CR1[
WE]
CR1[
SE]
CR0[FILTER
_CNT]
FPR[FILT_P
ER]
Operation
Maximum Latency¹
1
0
X
X
X
X
Disabled
N/A
2A
1
0
0
0x00
X
Continuous Mode
T_PD
2B
1
0
0
X
0x00
3A
1
0
1
0x01
X
Sampled, Non-Filtered mode
T_PD + T_SAMPLE + T_per
3B
1
0
0
0x01
> 0x00
T_PD + (FPR[FILT_PER] x
T_per) + T_per
4A
1
0
1
> 0x01
X
Sampled, Filtered mode T_PD + (CR0[FILTER_CNT] x
T_SAMPLE) + T_per
4B
1
0
0
> 0x01
> 0x00
T_PD + (CR0[FILTER_CNT] x
FPR[FILT_PER] x T_per) +
T_per
5A
1
1
0
0x00
X
Windowed mode
T_PD + T_per
5B
1
1
0
X
0x00
T_PD + T_per
6
1
1
0
0x01
0x01 - 0xFF
Windowed / Resampled
mode
T_PD + (FPR[FILT_PER] x
T_per) + 2T_per
Table continues on the next page...
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
880
Freescale Semiconductor, Inc.