Chapter 5
Interrupt Controller
V - 46 Noise Filter Function
5.4.7 Noise Filter Operation
■ Noise Filter Operation
Noise filters can be used for external interrupts by setting the NFCNTn flag of the noise filter control register
(NFCNT) to “1”. Each of these noise filter uses the sampling clock to count an external interrupt signal. The filter
recognizes such a signal as an interrupt and issues a signal to the internal interrupt controller if the same signal
level (“H” or “L”) is detected 3 times or more.
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Be sure to disable interrupts when specifying whether to enable or disable noise filters.
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Figure:5.4.2 Noise Filter Operation
■ Noise Filter Sampling Frequency Setup
Sampling clock set registers (NFCLK0, NFCLK1) can be used to select a sampling clock of noise filters. The
sampling clock can be selected from 1/4, 1/8, 1/16, and 1/32 of IOCLK.
■ Setup of Interrupt Generation Condition for External Interrupts
Generation condition for an external interrupt can be selected from 5 types: both-edge detection, rising edge, fall-
ing edge, H level, and L level. Edge detection registers (IRQEDGESEL) are used to set whether to enable or dis-
able both-edge detection; and, if setting disable both-edge detection, external interrupt condition specification
registers (EXTMD0, EXTMD1) are used to select the rising edge, falling edge, H level, and L level from. If set-
ting enable both-edge detection, the EXTMD0 and EXTMD1 registers are used to select the rising edge.
Sampling clock
Signal received
through interrupt pin
Interrupt signal sent
to internal interrupt
controller
"L" level detected 3 times
"H" level detected 3 times
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