Datasheet

16
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
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
pending interrupts, as shown in this example.
4.8.1 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 handling 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.
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) */