Ac Zero-Cross Detector; Registers - Panasonic F77G User Manual

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".
AC line waveform
V
DD
V
SS
Ideal
IRQ1
Actual
IRQ1
Figure 3-3-9
Actual IRQ1 interrupt request is generated several times at crossing the 1/2 V
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
Point A
AC Line Waveform and IRQ1 Generation Timing
approx.10 ms at 50 H
Z
approx.8.3 ms at 60 H
Z
of AC line wave-
DD