7545 datasheet(26/62 Pages) RENESAS

26 / 62 page

Rev.1.06

Mar 07, 2008

Page 26 of 59

REJ03B0140-0106

7545 Group

Timers

The 7545 Group has 3 timers: timer 1, timer 2 and timer 3.

The division ratio of every timer and prescaler is 1/(n+1)

provided that the value of the timer latch or prescaler is n.

All the timers are down count timers. When a timer reaches “0”,

a n underfl o w occurs at the n e xt co un t pu lse, and the

corresponding timer latch is reloaded into the timer. When a

timer underflows, the interrupt request bit corresponding to each

timer is set to “1”.

1. Timer 1

Timer 1 is an 8-bit timer and counts the prescaler 1 output.

When Timer 1 underflows, the timer 1 interrupt request bit is set

to “1”.

Prescaler 1 is an 8-bit prescaler and counts the clock which is

f(XIN) divided by 16.

Prescaler 1 and Timer 1 have the prescaler 1 latch and the timer 1

latch to retain the reload value, respectively. The value of

prescaler 1 latch is set to Prescaler 1 when Prescaler 1

underflows. The value of timer 1 latch is set to Timer 1 when

Timer 1 underflows.

When writing to Prescaler 1 (PRE1) is executed, the value is

written to both the prescaler 1 latch and Prescaler 1.

When writing to Timer 1 (T1) is executed, the value is written to

both the timer 1 latch and Timer 1.

When reading from Prescaler 1 (PRE1) and Timer 1 (T1) is

executed, each count value is read out.

Timer 1 always operates in the timer mode.

Prescaler 1 counts the clock which is f(XIN) divided by 16. 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.

Timer 1 counts the underflow signal of Prescaler 1. The contents

of Timer 1 is decremented by 1 each time the count clock 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.

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

2. Timer 2

Timer 2 is an 8-bit timer and counts the clock selected by the

timer 2 count source selection bit. When Timer 2 underflows, the

timer 2 interrupt request bit is set to “1”.

Timer 2 has two timer latches (primary latch and secondary

latch) to retain the reload value.

The value written to timer 2 primary (T2P) while timer 2 is

stopped is transferred to the timer 2 primary latch and the

counter.

The value written to timer 2 secondary (T2S) while timer 2 is

stopped is transferred only to timer 2 secondary latch.

After the count of timer 2 starts, the values written to timer 2

primary (T2P) and timer 2 secondary (T2S) are transferred only

to each latch. The values are not transferred to the counter at

write.

When each timer underflows, the values of timer 2 primary latch

and the timer 2 secondary latch are alternately 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 2 primary (T2P) is read, the count value of the timer

is read. When timer 2 secondary (T2S) is read, a set value of

timer 2 secondary is read. (Read the timer 2 primary to read the

count value even during the count period of timer 2 secondary.)

When the timer 2 primary is read, the count value of timer 2 is

read since the count value of the timer 2 is retained until writing

to timer 2 primary (T2P) is performed after timer 2 is stopped.

Timer 2 always operates in the timer mode.

Timer 2 counts the clock selected by the timer 2 count source

selection bit. The contents of Timer 2 is decremented by 1 each

time the count clock is input. When the contents of Timer 2 reach

“0016”, an underflow occurs at the next count clock, and the

timer 2 primary latch or timer 2 secondary latch is alternately

reloaded into Timer 2 and count continues.

7545 Datasheet(PDF) 26 Page - Renesas Technology Corp

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