Datasheet

14
7701F–AVR–10/12
Atmel ATtiny24/44/84 [Preliminary]
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.
5.8.1 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 four 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 (two bytes) is popped back from the stack, the stack pointer is
incremented by two, and the I-bit in SREG is set.
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
_SEI(); /* set Global Interrupt Enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */