7477 datasheet(252/354 Pages) RENESAS

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2-17

7470/7471/7477/7478 GROUP USER’S MANUAL

APPLICATION

2.3 Timers

7470

7471

7477

7478

Fig. 2.3.7 Example of control procedure [Piezoelectric buzzer output]

RESET

16 ! (124+1) ! 2

8 MHz

Set the interrupt disable flag (each interrupt disabled)

Clear the timer 1 interrupt enable bit

(Timer 1 interrupt disabled)

Set the Timer 12 mode register

!!! 1

1 T12M (Address 00F816)

Timer 1 count stop

Timer 1 count source

← Internal clock

Timer 1 internal clock count source

← f(XIN)/16

T0 output selected

Initialization

Set the Timer mode register 2

!! !

!!! !

1 TM2 (Address 00FA16)

Timer 1 division flip flop set enabled

Set the Timer FF register

!! !

!!! !

0 TF (Address 00F716)

Timer 1 division flip flop initial value 0

Set the port P12 as an output

Port P12

← “H”

Set the Timer 1 to “7C 16”

Set the Timer 1 interrupt enable bit

(Timer 1 interrupt enabled)

Clear the interrupt disable flag (each interrupt enabled)

Main processing

Output unit

A piezoeletric buzzer is requested ?

Y (= 0 Request)

N (= No request)

T Buzzer output stop

Port P12

← “H”

Set the Timer 1 to “7C 16”

T Buzzer output start

T A piezoelectric buzzer output stops.

T 2 kHz =

Fixed dividion ratio

Count by interrupt processing

Timer 1 overflow divided by 2

7C16

T A piezoelectric buzzer request generated in the

main processing is processed in the output unit.

Immediately after no request?

Set the Timer 12 mode register

0 0

!! ! 11 T12M (Address 00F816)

Timer 1 count stop

Set the Timer 12 mode register

!! ! 10 T12M (Address 00F816)

Timer 1 count start

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