4502 datasheet(137/214 Pages) RENESAS

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2.2 Interrupts

2-20

Rev.2.01

Feb 02, 2005

4502 Group

APPLICATION

REJ09B0193-0201

Fig. 2.2.4 Timer 2 constant period interrupt setting example

➀ Disable Interrupts

Timer 2 interrupt is temporarily disabled.

Interrupt enable flag INTE

Interrupt control register V1

“0”

✕✕ ✕

All interrupts disabled (DI instruction)

Timer 2 interrupt occurrence disabled

(TV1A instruction)

0 1

➁ Stop Timer 2 Operation

Timer 2 and prescaler are temporarily stopped.

Dividing ratio of prescaler is selected.

Timer control register W1

Prescaler stop (TW1A instruction)

Prescaler divided by 16 selected for count source

➂ Set Timer Value

Timer 2 count time is set. (The formula is shown ❈A below.)

Timer 2 reload register R2 “5216”

Timer count value 82 set (T2AB instruction)

➃ Clear Interrupt Request

Timer 2 interrupt activated condition is cleared.

Timer 2 interrupt request flag T2F “0”

Timer 2 interrupt activated condition cleared

(SNZT2 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 T2F, insert the NOP instruction after the SNZT2 instruction.

➄ Start Timer 2 Operation

Timer 2 and prescaler temporarily stopped are restarted.

Timer control register W1

Prescaler operation start (TW1A instruction)

b3b0

➅ Enable Interrupts

The timer 2 interrupt which is temporarily disabled is enabled.

Interrupt control register V1

“1”

Timer 2 interrupt occurrence enabled

(TV1A instruction)

All interrupts enabled (EI instruction)

✕✕ ✕

Constant period interrupt execution start

❈A The prescaler dividing ratio and timer 2 count value to make the interrupt occur

every about 1 ms are set as follows.

1 ms

≅ (4.0 MHz) ✕ 3

✕ 16

✕ (82+1)

–1

System clock Instruction

clock

Prescaler

dividing

ratio

Timer

2count

value

“✕”: it can be “0” or “1.”

Timer control register W2

Timer 2 stop (TW2A instruction)

Prescaler output selected for count source

✕✕

b3b0

Timer control register W2Timer 2 operation start (TW2A instruction)

Interrupt enable flag INTE

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