Datasheet

C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before
any pending interrupts, as shown in the following example.
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) */
Related Links
Memory Programming on page 327
Interrupts on page 62
BTLDR - Boot Loader Support – Read-While-Write Self-Programming on page 311
10.7.1. Interrupt Response Time
The interrupt execution response for all the enabled Atmel AVR interrupts is four clock cycles minimum.
After four clock cycles, the Program Vector address for the actual interrupt handling routine is executed.
During this 4-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
four 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 four clock cycles. During these four clock cycles, the
Program Counter (2 bytes) is popped back from the Stack, the Stack Pointer is incremented by 2, and the
I-bit in SREG is set.
Atmel ATmega32A [DATASHEET]
Atmel-8155I-ATmega32A_Datasheet_Complete-08/2016
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