AT90USB646 datasheet(70/456 Pages) ATMEL

70 / 456 page

7593L–AVR–09/12

AT90USB64/128

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 Section “Memory programming” on page 359 for details.

To avoid unintentional changes of Interrupt Vector tables, a special write procedure must be fol-

lowed to change the IVSEL bit:

Write the Interrupt Vector Change Enable (IVCE) bit to one.

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

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. Refer to the section “Memory programming” on page 359

for details on Boot Lock bits.

• 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

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)

{

unsigned char temp;

/* Get MCUCR */

temp = MCUCR;

/* Enable change of Interrupt Vectors */

MCUCR = temp | (1<<IVCE);

/* Move interrupts to Boot Flash section */

MCUCR = temp | (1<<IVSEL);

}

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