Chapter 7 AC Zero-Cross Circuit/Noise Filter

7-2 AC Zero-Cross Circuit Operation

7-2-1 Setup and Operation

Settings for zero-cross circuit operation are listed below.

(1)Set the REDG1 flag of the IRQ1ICR register to select the valid edge for IRQ1.

(2)Set the NF1EN and NF1CK1 to 0 flags of the NFCTR register to set the noise filter and its sampling clock.

(3)With the P21IM flag of the FLOAT1 register, set the P21 pin to zero-cross detection.

(4)An IRQ1 interrupt is generated by the falling edge or the rising edge of AC zero-cross detection output.

10 ms at 50Hz

8.3 ms at 60Hz

AC line waveform

VDD

VSS

Ideal

IRQ1

Actual

IRQ1

Point A

Figure 7-2-1 AC Line Waveform and IRQ Generation Timing

Actual IRQ interrupt requests will be generated multiple times. Therefore, the software must filter this signal before making any evaluations.

When noise filtering is selected for use, the amount of evaluation processing by the software will be reduced. However, if the OSC stops, a return from the backup mode will not be possible.

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Panasonic MN101C00 user manual AC Zero-Cross Circuit Operation, AC Line Waveform and IRQ Generation Timing