Chapter 3 InterruptsIII - 54 External Interrupts3-3-8 AC Zero-Cross DetectorThis LSI has AC zero-cross detector circuit. The P21 / ACZ pin is the input pin of AC zero-cross detectorcircuit. AC zero-cross detector circuit output the high level when the input level is at the middle, andoutputs 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 atintermediate range. At the other level, IRQ1 pin is set to the low level. AC zero-cross can be detected bysetting the P21IM flag of the noise filter control register (NFCTR) to "1".V DDV SSAC line waveformPoint AIdealIRQ1ActualIRQ1approx.10 ms at 50 H Zapprox.8.3 ms at 60 H ZFigure 3-3-9 AC Line Waveform and IRQ1 Generation TimingThe 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.
