ATmega324P datasheet(16/377 Pages) ATMEL

16 / 377 page

7674F–AVR–09/09

ATmega164P/324P/644P

When the AVR exits from an interrupt, it will always return to the main program and execute one

more instruction before any pending interrupt is served.

Note that the Status Register is not automatically stored when entering an interrupt routine, nor

restored when returning from an interrupt routine. This must be handled by software.

When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.

No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the

CLI instruction. The following example shows how this can be used to avoid interrupts during the

timed EEPROM write sequence..

When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-

cuted before any pending interrupts, as shown in this example.

Assembly Code Example

r16, SREG

; store SREG value

cli

; disable interrupts during timed sequence

sbi

EECR, EEMPE

; start EEPROM write

sbi

EECR, EEPE

out

SREG, r16

; restore SREG value (I-bit)

C Code Example

char

cSREG;

cSREG = SREG; /* store SREG value */

/* disable interrupts during timed sequence */

__disable_interrupt();

EECR |= (1<<EEMPE); /* start EEPROM write */

EECR |= (1<<EEPE);

SREG = cSREG; /* restore SREG value (I-bit) */

Assembly Code Example

sei

; set Global Interrupt Enable

sleep

; enter sleep, waiting for interrupt

; note: will enter sleep before any pending

; interrupt(s)

C Code Example

__enable_interrupt(); /* set Global Interrupt Enable */

__sleep(); /* enter sleep, waiting for interrupt */

/* note: will enter sleep before any pending interrupt(s) */

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