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R01UH0336EJ0102 Rev.1.02
Page 103 of 1538
Jul 17, 2014
V850E2/PG4-L
Section 2 Port Functions
2.14 Cancelling Noise on Pins
This section describes the noise-filtering insertion pin, filter groups, noise-
cancellation sampling clock, and control registers.
2.14.1
Details of Noise Cancellation
(1)
Digital Filter Function
The input signal is sampled with the sampling frequency fs.
If the input is sampled at the same level in a specified number of successive
samples, the signal level is judged as valid and the filter output signal is
changed accordingly.
If the external signal level changes within the specified number of samples (at
the same level), the new signal level is judged to be noise–or a spike–and the
level of the output signal from the filter does not change.
The length of an external signal pulse to be judged as noise depends on the
sampling frequency and the specified number of same level samples.
Both parameters can be specified.
• DNFAnCTL.DNFAnPRS[2:0] allows to select the sampling frequency to
fs = f
DNFATCKI
/ 2
DNFAnPRS[2:0]
where f
DNFATCKI
is the frequency of the DNFATCKI clock.
• DNFAnCTL.DNFAnNFSTS[1:0] specifies the number (2 to 5) of same level
samples.
External signal pulses shorter than.
(DNFAnNFSTS[1:0] -1) × 1/fs
Caution
If noise is sampled as the same level over the specified number of successive
samples, the noise will not be cancelled.
External signal pulses longer than
DNFAnNFSTS[1:0] × 1/fs
are always judged to be valid and passed on to the filter output.
External signal pulses with a width between
(DNFAnNFSTS[1:0] – 1) × 1/fs and DNFAnNFSTS[1:0] × 1/fs
may be eliminated or judged to be valid.