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Chapter 3    Interrupts

III - 54

External Interrupts

This LSI has AC zero-cross detector circuit. The P21 / ACZ pin is the input pin of AC zero-cross detector

circuit. AC zero-cross detector circuit output the high level when the input level is at the middle, and

outputs the low level at other level.

■

AC Zero-Cross Detector (External interrupt 1)

AC zero-cross detector sets the IRQ1 pin to the high level when the input signal (P21/ACZ pin) is at

intermediate range. At the other level, IRQ1 pin is set to the low level. AC zero-cross can be detected by

setting the P21IM flag of the noise filter control register (NFCTR) to "1".

V

DD

V

SS

AC line waveform

Point A

Ideal
IRQ1

Actual
IRQ1

approx.10 ms at 50 H

Z

approx.8.3 ms at 60 H

Z

The interrupt request is generated at the rising edge of the AC zero-cross detector signal.

Actual IRQ1 interrupt request is generated several times at crossing the 1/2 V

DD

 of AC line wave-

form. So, the filtering operation by the program is needed.