7540 datasheet(122/366 Pages) RENESAS

122 / 366 page

2-46

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

APPLICATION

7540 Group

2.4 Timer X

2.4.3 Timer mode

(1) Operation description

Prescaler X counts the selected count source by the timer X count source selection bits. Each time

the count clock is input, the contents of Prescaler X is decremented by 1. When the contents of

Prescaler X reach “0016”, an underflow occurs at the next count clock, and the prescaler X latch is

reloaded into Prescaler X and count continues. The division ratio of Prescaler X is 1/(n+1) provided

that the value of Prescaler X is n.

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

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

timer X latch is reloaded into Timer X and count continues. The division ratio of Timer X is 1/(m+1)

provided that the value of Timer X is m. Accordingly, the division ratio of Prescaler X and Timer X

is provided as follows that the value of Prescaler X is n and the value of Timer X is m.

Timer X can stop counting by setting “1” to the timer X count stop bit.

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

(2) Timer mode setting method

Figure 2.4.10 shows the setting method for timer mode of timer X.

Division ratio =

(n+1) ✕ (m+1)

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