Panasonic MN101C77C, F77G AC Zero-Cross Detector, AC Line Waveform and IRQ1 Generation Timing

Chapter 3 Interrupts

3-3-8 AC Zero-Cross Detector

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".

approx.10 ms at 50 HZ approx.8.3 ms at 60 HZ

AC line waveform

VDD

VSS

Ideal

IRQ1

Actual

IRQ1

Point A

Figure 3-3-9 AC Line Waveform and IRQ1 Generation Timing

Actual IRQ1 interrupt request is generated several times at crossing the 1/2 VDD of AC line wave- form. So, the filtering operation by the program is needed.

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

III- 54 External Interrupts