Latency Issues - NXP Semiconductors freescale KV4 Series Reference Manual

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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 all the consecutive

CR0[FILTER_CNT] samples agree that the output value has changed.

35.4.4.2 Latency issues

The value of FPR[FILT_PER] or SAMPLE period must be set such that the sampling

period is just longer than the period of the expected noise. This way a noise spike will

corrupt only one sample. The value of CR0[FILTER_CNT] must 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 power of CR0[FILTER_CNT].

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 power of

CR0[FILTER_CNT].

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.

Table 35-38. Comparator sample/filter maximum latencies

Freescale Semiconductor, Inc.

KV4x Reference Manual, Rev. 2, 02/2015

Chapter 35 Comparator (CMP)

Continuous Mode

Sampled, Non-Filtered mode

Sampled, Filtered mode

Windowed mode

Windowed / Resampled

Windowed / Filtered mode

Maximum latency

+ (FPR[FILT_PER] *

+ (CR0[FILTER_CNT] *

+ (CR0[FILTER_CNT] *

FPR[FILT_PER] x T

+ (FPR[FILT_PER] *

+ (CR0[FILTER_CNT] *

FPR[FILT_PER] x T