7545 datasheet(27/62 Pages) RENESAS

27 / 62 page

Rev.1.06

Mar 07, 2008

Page 27 of 59

REJ03B0140-0106

7545 Group

3. Timer 3

Timer 3 is an 8-bit timer and counts the clock selected by the

timer 3 count source selection bit. When Timer 3 underflows, the

timer 3 interrupt request bit is set to “1”.

Timer 3 has a timer latch to retain the reload value.

The value written to timer 3 (T3) while timer 3 is stopped is

transferred to the timer latch and the counter.

After the count of timer 3 (T3) starts, the value written to timer 3

is transferred only to the timer 3 latch. The value is not

transferred to the counter at write.

When timer underflows, the value of timer 3 latch is transferred

to the counter. (Since a count value of a timer is retained, the

written value becomes the count value of the timer after the next

underflow.)

When timer 3 (T3) is read, the count value of the timer is read.

When the timer 3 is read, the count value of timer 3 is read since

the count value of the timer 3 is retained until writing to timer 3

(T3) is performed after timer 3 is stopped.

Timer 3 always operates in the timer mode.

Timer 3 counts the clock selected by the timer 3 count source

selection bit. The contents of Timer 3 is decremented by 1 each

time the count clock is input.

The division ratio of Timer 3 is 1/(n+1) provided that the value

of Timer 3 is n.

Timer 3 is stopped by setting “1” to the timer 3 count stop bit.

Timer 2 and timer 3 are also used for the control timer of the

carrier wave control circuit.

Fig. 22 Structure of timer count source set register

Fig. 23 Timer 1, 2, 3 control register

Timer count source set register

(TCSS : address 002A16, initial value: 0016)

Timer 2 count source selection bits

b1 b0

0 : f(XIN)/16

1 : f(XIN)/2

0 : f(XIN)/8

1 : f(XIN)/1

Disable (return “0” when read)

Timer 3 count source selection bits

b3 b2

0 : f(XIN)/16

1 : f(XIN)/2

0 : f(XIN)/8

1 : Carrier wave output (CARRY)

Timer 1, 2, 3 control register

(TC123 : address 002B16, initial value: 0616)

Timer 1 count stop bit

0: Count start

1: Count stop

Timer 2 count stop bit

0: Count start

1: Count stop

Timer 3 count stop bit

0: Count start

1: Count stop

Disable (return “0” when read)

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