H838532H datasheet(273/508 Pages) RENESAS

273 / 508 page

Section 9 Timers

Rev. 1.00 May 30, 2008 Page 253 of 484

REJ09B0436-0100

9.5.3

Noise Canceler

The noise canceler consists of a digital low-pass filter that eliminates high-frequency component

noise from the pulses input from the input capture input pin. The noise canceler is set by NCS* in

PMR3.

Figure 9.9 shows a block diagram of the noise canceler.

Latch

Match

detector

Noise

canceler

output

Sampling

clock

Input capture

input signal

Sampling clock

∆t: Set by CKS1 and CKS0

Figure 9.9 Noise Canceler Block Diagram

The noise canceler consists of five latch circuits connected in series and a match detector circuit.

When the noise cancellation function is not used (NCS = 0), the system clock is selected as the

sampling clock. When the noise cancellation function is used (NCS = 1), the sampling clock is the

internal clock selected by CKS1 and CKS0 in TMG, the input capture input is sampled on the

rising edge of this clock, and the data is judged to be correct when all the latch outputs match. If

all the outputs do not match, the previous value is retained. After a reset, the noise canceler output

is initialized when the falling edge of the input capture input signal has been sampled five times.

Therefore, after making a setting for use of the noise cancellation function, a pulse with at least

five times the width of the sampling clock is a dependable input capture signal. Even if noise

cancellation is not used, an input capture input signal pulse width of at least 2

φ or 2φ

SUB is

necessary to ensure that input capture operations are performed properly

Note: *

An input capture signal may be generated when the NCS bit is modified.

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