4501 datasheet(135/212 Pages) RENESAS

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2.2 Interrupts

2-18

Rev.2.01

Feb 07, 2005

4501 Group

APPLICATION

REJ09B0192-0201

Fig. 2.2.3 Timer 1 constant period interrupt setting example

b3b0

0 1

b3b0

➀ Disable Interrupts

Timer 1 interrupt is temporarily disabled.

Interrupt enable flag INTE

Interrupt control register V1

“0”

✕✕ ✕

All interrupts disabled (DI instruction)

Timer 1 interrupt occurrence disabled

(TV1A instruction)

➁ Stop Timer Operation

Timer 1 and prescaler are temporarily stopped.

Dividing ratio of prescaler is selected.

Timer control register W1

Timer 1 stop (TW1A instruction)

Prescaler stop

Prescaler divided by 16 selected

➂ Set Timer Value

Timer 1 count time is set. (The formula is shown ❈A below.)

Timer 1 reload register R1 “5216”

Timer count value 82 set (T1AB instruction)

➃ Clear Interrupt Request

Timer 1 interrupt activated condition is cleared.

Timer 1 interrupt request flag T1F “0”

Timer 1 interrupt activated condition cleared

(SNZT1 instruction)

Note when the interrupt request is cleared

When ➃ is executed, considering the skip of the next instruction according to the

interrupt request flag T1F, insert the NOP instruction after the SNZT1 instruction.

➄ Start Timer Operation

Timer 1 and prescaler temporarily stopped are restarted.

Timer control register W1

Timer 1 operation start (TW1A instruction)

Prescaler operation start

➅ Enable Interrupts

The Timer 1 interrupt which is temporarily disabled is enabled.

Interrupt control register V1

Interrupt enable flag INTE

“1”

Timer 1 interrupt occurrence enabled

(TV1A instruction)

All interrupts enabled (EI instruction)

✕✕ ✕

Constant period interrupt execution start

❈A The prescaler dividing ratio and timer 1 count value to make the interrupt occur every 1 ms are set as follows.

1 ms

≅ (4.0 MHz) ✕ 3

✕ 16

✕ (82+1)

–1

System clock Instruction

clock

Prescaler

dividing

ratio

Timer 1

count

value

“✕”: it can be “0” or “1.”

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