Datasheet

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

neously 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 pending interrupts, as shown in this example.

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is five clock cycles

minimum. After five clock cycles the program vector address for the actual interrupt han-

dling routine is executed. During these five clock cycle period, the Program Counter is

pushed onto the Stack. The vector is normally a jump to the interrupt routine, and this

jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle

instruction, this instruction is completed before the interrupt is served. If an interrupt

occurs when the MCU is in sleep mode, the interrupt execution response time is

increased by five clock cycles. This increase comes in addition to the start-up time from

the selected sleep mode.

A return from an interrupt handling routine takes five clock cycles. During these five

clock cycles, the Program Counter (three bytes) is popped back from the Stack, the

Stack Pointer is incremented by three, and the I-bit in SREG is set.

Assembly Code Example

in 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) */