3819 datasheet(166/218 Pages) RENESAS

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2. APPLICATION

MITSUBISHI MICROCOMPUTER

3819 Group

2.7 Zero cross detection circuit

3819 Group USER’S MANUAL

2.7.4 Zero cross detection circuit application example 2

Clock count using ZCR interrupt (using a noise filter)

Outline : The clock is counted up every second by using the ZCR interrupts.

Specifications : • f(XIN)=4 MHz

• The noise filter (sampling clock : f(XIN)/256) is used.

(Pulse less than 64

µs is eliminated as a noise.)

• The commercial frequency (50 Hz or 60 Hz) is input.

• The clock is counted up by using the ZCR interrupts.

Figure 2.7.8 shows a setting of related registers.

Fig. 2.7.8 Setting of related registers [Clock count using ZCR interrupt (using a noise filter)]

ZCR active edge : Falling edge active (Note)

INTEDGE

Interrupt edge selection register (Address:3A16)

IREQ1

Interrupt request register 1 (Address:3C16)

Set the INT1/ZCR interrupt request bit to “0”

ICON1

Interrupt control register 1 (Address:3E16)

INT1/ZCR interrupt : Enabled

IREQ1

Interrupt request register 1 (Address:3C16)

ZCR interrupt request

Passing through the zero cross detection circuit (Note)

ZCRCON

Zero cross detection control register (Address:3916)

1 1

Noise filter sampling clock : f(XIN)/256

Selection of one-sided edge detection

When changing the values of bit 0 of the zero cross detection control register and bit 1 of the

interrupt edge selection register, make sure the following contents.

1. During changeing, set bit 1 of the interrupt control register 1 (disable ZCR interrupt) to “0”.

2. After changeing, set bit 1 of the interrupt request register 1 (no ZCR interrupt request) to “0”.

However, the value of bit 1 of the interrupt request register 1 is changed with a maximum delay

of 2 sampling clocks by using a noise filter. Thus, after changing, set this bit to “0” after a wait

of 2 sampling clocks.

Note :

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