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Chapter 3 Interrupts
External Interrupts
3-3-7 Noise Filter
■Noise Filter (External interrupts 0 to1)
Noise filter reduce noise by sampling the input waveform from the external interrupt pins (IRQ0, IRQ1).
Its sampling cycle can be selected from 4 types (fosc, fosc/2
8
, fosc/2
9
, fosc/2
10
).
■Noise Remove Selection (External interrupts 2 to 4)
Noise filter reduce noise by sampling the input waveform from the external interrupt pins (IRQ2 to IRQ4). Its
sampling cycle is fosc.
■Noise Remove Selection (External interrupts 0 to 4)
Noise remove function can be selected by setting the NFnEN flag of the noise filter control register
(NFCTR) to "1".
■Sampling Cycle Setup (External interrupts 0 and 1)
The sampling cycle of noise remove function can be set by the NFnSCK 1- 0 flag of the NFCTR register.
Table 3-3-3 Noise Remove Function
Table 3-3-4 Sampling Cycle / Time of Noise Remove Function
NFnEN 0 1
IRQ0 input (P20) IRQ0 Noise filter OFF IRQ0 Noise filter ON
IRQ1 input (P21) IRQ1 Noise filter OFF IRQ1 Noise filter ON
IRQ2 input (P22) IRQ2 Noise filter OFF IRQ2 Noise filter ON
IRQ3 input (P23) IRQ3 Noise filter OFF IRQ3 Noise filter ON
IRQ4 input (P24) IRQ4 Noise filter OFF IRQ4 Noise filter ON
Sampling
cycle
0 fosc 20 MHz 50 ns 8 MHz 125 ns
1
fosc/2
8
78.13 kHz 12.80
µ
s 31.25 kHz 32
µ
s
0
fosc/2
9
39.06 kHz 25.60
µ
s 15.62 kHz 64
µ
s
1
fosc/2
10
19.53 kHz 51.20
µ
s 7.81 kHz 128
µ
s
High-Speed oscillation
fosc=20 MHz fosc=8 MHz
NFnCKS1 NFnCKS0
0
1