7540 datasheet(115/366 Pages) RENESAS

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REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

7540 Group

APPLICATION

2.3 Timer 1

2.3.3 Timer 1 operation description

Timer 1 always operates in the timer mode.

Prescaler 1 counts the selected count source. Each time the count clock is input, the contents of Prescaler

1 is decremented by 1.

When the contents of Prescaler 1 reach “0016”, an underflow occurs at the next count clock, and the

prescaler 1 latch is reloaded into Prescaler 1 and count continues. The division ratio of Prescaler 1 is 1/

(n+1) provided that the value of Prescaler 1 is n.

The contents of Timer 1 is decremented by 1 each time the underflow signal of Prescaler 1 is input. When

the contents of Timer 1 reach “0016”, an underflow occurs at the next count clock, and the timer 1 latch

is reloaded into Timer 1 and count continues. The division ratio of Timer 1 is 1/(m+1) provided that the

value of Timer 1 is m. Accordingly, the division ratio of Prescaler 1 and Timer 1 is provided as follows that

the value of Prescaler 1 is n and the value of Timer 1 is m.

Timer 1 cannot stop counting by software.

Also, when timer 1 underflows, the timer 1 interrupt request bit is set to “1”.

2.3.4 Notes on timer 1

Note on using timer 1 is described below.

(1) Notes on set of the oscillation stabilizing time

Timer 1 can be used to set the oscillation stabilizing time after release of the STP instruction. The

oscillation stabilizing time after release of STP instruction can be selected from “set automatically”/

“not set automatically” by the oscillation stabilizing time set bit after release of the STP instruction

of MISRG. When “0” is set to this bit, “0116” is set to timer 1 and “FF16” is set to prescaler 1

automatically. When “1” is set to this bit, nothing is set to timer 1 and prescaler 1. Therefore, set the

wait time according to the oscillation stabilizing time of the oscillation. Also, when timer 1 is used,

set values again to timer 1 and prescaler 1 after system is returned from the stop mode.

Division ratio =

(n+1) ✕ (m+1)

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