Panasonic MN101C77C - Manual (Page 148)

Chapter 3 Interrupts
III - 54 External 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".
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
Figure 3-3-9 AC Line Waveform and IRQ1 Generation Timing
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.