PCINT15 datasheet(18/294 Pages) ATMEL

18 / 294 page

9219A–RFID–01/11

Atmel ATA5505 [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.

2.7.2

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) */

PCINT15 Datasheet(PDF) 18 Page - ATMEL Corporation