AT90USB646 datasheet(71/434 Pages) ATMEL

71 / 434 page

7593A–AVR–02/06

AT90USB64/128

Note:

1. The Boot Reset Address is shown in Table 28-8 on page 366. For the BOOTRST Fuse “1”

means unprogrammed while “0” means programmed.

9.1.1

Moving Interrupts Between Application and Boot Space

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

9.1.2

MCU Control Register – MCUCR

• 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 “Memory Programming” on page 368 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

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 pro-

grammed, 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 dis-

abled while executing from the Boot Loader section. Refer to the section “Memory Programming”

on page 368 for details on Boot Lock bits.

• Bit 0 – IVCE: Interrupt Vector Change Enable

Table 9-2.

Reset and Interrupt Vectors Placement

(1)

BOOTRST

IVSEL

Reset Address

Interrupt Vectors Start Address

0x0000

0x0002

0x0000

Boot Reset Address + 0x0002

Boot Reset Address

0x0002

Boot Reset Address

Boot Reset Address + 0x0002

Bit

JTD

–

PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

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