ATmega16HVB datasheet(56/273 Pages) ATMEL

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8042A–AVR–07/09

ATmega16HVB/32HVB

12.3

Moving Interrupts Between Application and Boot Space

The General Interrupt Control Register controls the placement of the Interrupt Vector table.

12.4

12.4.1

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 191 for details. To avoid unintentional changes of Interrupt Vector

tables, a special write procedure must be followed 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

Assembly Code Example

Move_interrupts:

; Enable change of Interrupt Vectors

ldi

r16, (1<<IVCE)

out

MCUCR, r16

; Move interrupts to Boot Flash section

ldi

r16, (1<<IVSEL)

out

MCUCR, r16

ret

C Code Example

void

Move_interrupts(void)

{

/* Enable change of Interrupt Vectors */

MCUCR = (1<<IVCE);

/* Move interrupts to Boot Flash section */

MCUCR = (1<<IVSEL);

}

Bit

76543

210

0x35 (0x55)

JTD

–

PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

00000

000

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