NXP Semiconductors freescale K51 Series Reference Manual

If CR1[SE]=1, the filter takes samples of COUTA on each positive transition of thesample input. The output state of the filter changes when CR0[FILTER_CNT]consecutive samples all agree that the output value has changed.32.8.4.2 Latency IssuesThe FPR[FILT_PER] value (or SAMPLE period) should be set such that the samplingperiod is just larger than the period of the expected noise. This way a noise spike willonly corrupt one sample. The CR0[FILTER_CNT] value should be chosen to reduce theprobability of noisy samples causing an incorrect transition to be recognized. Theprobability of an incorrect transition is defined as the probability of an incorrect sampleraised to the CR0[FILTER_CNT] power.The following table summarizes maximum latency values for the various modes ofoperation in the absence of noise. Filtering latency is restarted each time an actual outputtransition is masked by noise.The values of FPR[FILT_PER] (or SAMPLE period) and CR0[FILTER_CNT] must alsobe traded off against the desire for minimal latency in recognizing actual comparatoroutput transitions. The probability of detecting an actual output change within thenominal latency is the probability of a correct sample raised to the CR0[FILTER_CNT]power.Table 32-30. Comparator Sample/Filter Maximum LatenciesMode # CR1[EN]CR1[WE]CR1[SE]CR0[FILTER_CNT]FPR[FILT_PER] Operation Maximum Latency11 0 X X X X Disabled N/A2A 1 0 0 0x00 X Continuous Mode TPD2B 1 0 0 X 0x003A 1 0 1 0x01 X Sampled, Non-Filtered mode TPD + TSAMPLE + Tper3B 1 0 0 0x01 > 0x00 TPD + (FPR[FILT_PER] xTper) + Tper4A 1 0 1 > 0x01 X Sampled, Filtered mode TPD + (CR0[FILTER_CNT] xTSAMPLE) + Tper4B 1 0 0 > 0x01 > 0x00 TPD + (CR0[FILTER_CNT] xFPR[FILT_PER] x Tper) +Tper5A 1 1 0 0x00 X Windowed mode TPD + Tper5B 1 1 0 X 0x00 TPD + Tper6 1 1 0 0x01 0x01 - 0xFF Windowed / ResampledmodeTPD + (FPR[FILT_PER] xTper) + 2TperTable continues on the next page...CMP Functional DescriptionK51 Sub-Family Reference Manual, Rev. 6, Nov 2011784 Freescale Semiconductor, Inc.