7549 datasheet(29/86 Pages) RENESAS

29 / 86 page

Rev.2.02

Mar 31, 2009

Page 27 of 81

REJ03B0202-0202

7549 Group

Timers

The 7549 Group has two 8-bit timers (timer 1 and timer 2) and

one 16-bit timer (timer A).

Timer 1 and timer 2 share the same 8-bit prescaler (prescaler 12).

Each timer and prescaler has a separate timer latch and prescaler

latch.

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

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

The timers decrement at each count clock input. When the count

value reaches “0”, an underflow occurs at the next count pulse.

The value of the corresponding timer latch is reloaded into the

timer at underflow and counting is continued. When a timer

underflow occurs, the interrupt request bit corresponding to each

timer is set to “1”.

• Prescaler 12 (PRE12)

Prescaler 12 is an 8-bit prescaler that counts the signal selected

by the prescaler 12 count source selection bit. The count source

can be selected from

φSOURCE/16 and XCIN input clock.

Writing to prescaler 12 writes the value to both the prescaler

latch and prescaler.

Reading from prescaler 12 reads the prescaler 12 count value.

The initial value is set to “FF16” after reset.

The division ratio of prescaler 12 is 1/(n+1), where n is the

setting value.

Prescaler 12 cannot stop counting by software.

• Timer 1 (T1)

Timer 1 is an 8-bit timer that counts the prescaler 12 output.

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

to “1”.

Writing to timer 1 writes the value to both the timer 1 latch and

timer 1.

Reading from timer 1 reads the timer 1 count value. The initial

value is set to “0116” after reset.

The division ratio of timer 1 is 1/(m+1), where m is the setting

value. This gives that the division ratio of prescaler 12 and timer

1 is 1/((n+1)

× (m+1)), where n is the prescaler 12 setting value

and m is the timer 1 setting value.

Timer 1 cannot stop counting by software.

• Timer 2 (T2)

Timer 2 is an 8-bit timer that counts the signal selected by the

timer 2 count source selection bit.

The count source can be selected from among

φSOURCE/16,

/256, prescaler 12 output, and timer A output signal.

Timer 2 counts the selected count source and sets the timer 2

interrupt request bit to “1” at underflow.

When writing to timer 2, the value of the timer 2 write control bit

can be used to select a write to both the timer 2 latch and timer 2

or a write to only the timer 2 latch.

Reading from timer 2 reads the timer 2 count value.

Timer 2 starts counting from “FF16” after reset.

The division ratio of timer 2 is 1/(n+1), where n is the timer 2

setting value. Timer 2 stops when the timer 2 count stop bit is set

to “1”.

When the P13/T2OUT output valid bit is set to “1”, the polarity of

the waveform output from the P13/T2OUT pin can be inverted at

each timer 2 underflow. The output start level of the T2OUT pin

can be selected using the T2OUT polarity switch bit. When this

bit is set to 0, the output starts at “H” level. When this bit is set to

“1”, the output starts at “L” level.

•Notes

(1) Reading from and Writing to Timer 1 and 2 and Prescaler 12

If the timer/prescaler count source clock and

φSOURCE are

different clocks, the timers and prescaler cannot be read or

written. Select the same clock to enable read and write

operations.

Note that timer 2 can be read and written even using a

different clock while its counting is stopped.

1Prescaler 12 and timer 1 cannot be read/written in the

following conditions:

Prescaler 12 count source: XCIN input clock

φSOURCE: Clock other than XCIN input clock

2Timer 2 cannot be read/written during counting in the

following conditions:

Timer 2 count source: Prescaler 12

Prescaler 12 count source: XCIN input clock

φSOURCE: Clock other than XCIN input clock

Timer 2 count source: Timer A underflow

Timer A count source: XCIN input clock

φSOURCE: Clock other than XCIN input clock

Timer 2 count source: Timer A underflow

Timer A count source: low-speed on-chip oscillator

output

φSOURCE: Clock other than low-speed on-chip

oscillator

(2) Count Source of Prescaler 12

The XCIN input clock can be selected as the prescaler count

source only if the 32 kHz quartz crystal oscillator is selected

by the oscillation method selection bit in FSROM1.

7549 Datasheet(PDF) 29 Page - Renesas Technology Corp

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