ATmega16 datasheet(13/315 Pages) ATMEL

13 / 315 page

ATmega16(L)

2466E–AVR–10/02

When using the SEI instruction to enable interrupts, the instruction following SEI will be

executed before any pending interrupts, as shown in this example.

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 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) */

ATMEGA16 Datasheet(PDF) 13 Page - ATMEL Corporation