Datasheet
11.7.1 Interrupt Response Time
The interrupt execution response for all the enabled 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 microcontroller (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.
ATmega48PA/88PA/168PA
AVR CPU Core
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Datasheet Complete
DS40002011A-page 38