4553 datasheet(28/145 Pages) RENESAS

28 / 145 page

Rev.3.02

Dec 22, 2006

page 28 of 142

REJ03B0024-0302

4553 Group

TIMERS

The 4553 Group has the following timers.

• Programmable timer

The programmable timer has a reload register and enables the

frequency dividing ratio to be set. It is decremented from a set-

ting value n. When it underflows (count to n + 1), a timer interrupt

request flag is set to “1,” new data is loaded from the reload reg-

ister, and count continues (auto-reload function).

• Fixed dividing frequency timer

The fixed dividing frequency timer has the fixed frequency divid-

ing ratio (n). An interrupt request flag is set to “1” after every n

count of a count pulse.

Fig. 21 Auto-reload function

The 4553 Group timer consists of the following circuits.

• Prescaler : 8-bit programmable timer

• Timer 1 : 8-bit programmable timer

• Timer 2 : 8-bit programmable timer

• Timer 3 : 16-bit fixed dividing frequency timer

• Timer LC : 4-bit programmable timer

• Watchdog timer : 16-bit fixed dividing frequency timer

(Timers 1, 2, and 3 have the interrupt function, respectively)

Prescaler and timers 1, 2, 3 and LC can be controlled with the

timer control registers PA, W1 to W4. The watchdog timer is a free

counter which is not controlled with the control register.

Each function is described below.

FF16

0016

n : Counter initial value

Count starts

Reload

1st underflow

2nd underflow

n+1 count

Time

An interrupt occurs or

a skip instruction is executed.

Timer interrupt

request flag

“1”

“0”

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