Datasheet

1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled in the
cycle IVCE is set, and they remain disabled until after the instruction following the write to IVSEL. If
IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status Register is
unaffected by the automatic disabling.
Note: If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is
programmed, interrupts are disabled while executing from the Application section. If Interrupt Vectors are
placed in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while
executing from the Boot Loader section.
Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by hardware
four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disable interrupts, as
explained in the IVSEL description above. See Code Example below.
Assembly Code Example
Move_interrupts:
; Get MCUCR
in r16, MCUCR
mov r17, r16
; Enable change of Interrupt Vectors
ori r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ori r17, (1<<IVSEL)
out MCUCR, r17
ret
C Code Example
void Move_interrupts(void)
{
uchar temp;
/* GET MCUCR*/
temp = MCUCR;
/* Enable change of Interrupt Vectors */
MCUCR = temp|(1<<IVCE);
/* Move interrupts to Boot Flash section */
MCUCR = temp|(1<<IVSEL);
}
Atmel ATmega644PA [DATASHEET]
Atmel-42717C-ATmega644PA_Datasheet_Complete-10/2016
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