ATmega169P datasheet(60/393 Pages) ATMEL

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8018N–AVR–08/09

ATmega169P

11.2.1

MCUCR – MCU Control Register

• Bit 1 – IVSEL: Interrupt Vector Select

When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash

memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot

Loader section of the Flash. The actual address of the start of the Boot Flash Section is deter-

mined by the BOOTSZ Fuses. Refer to the section ”Boot Loader Support – Read-While-Write

Self-Programming” on page 279 for details.

• 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 description in ”Moving Interrupts Between Application and Boot

Space” on page 59. See Code Example.

Assembly Code Example

Move_interrupts:

; Get MCUCR

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);

}

Bit

543210

0x35 (0x55)

JTD

PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

000000

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