ATMEGA640 datasheet(18/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

flag is cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable bit

is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the Global Interrupt Enable bit is

set, and will then be executed by order of priority.

The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not nec-

essarily have Interrupt Flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will

not be triggered.

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 executed before any pend-

ing 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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