ATmega32U2 datasheet(65/314 Pages) ATMEL

65 / 314 page

7799B–AVR–07/09

ATmega8U2/16U2/32U2

Notes:

1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at

reset, see “Memory Programming” on page 246.

2. When the IVSEL bit in MCUCR is set, Interrupt Vectors will be moved to the start of the Boot

Flash Section. The address of each Interrupt Vector will then be the address in this table

added to the start address of the Boot Flash Section. Moreover, contrary to other 8K/16K

devices, the interrupt vectors spacing remains identical (2 words) for both 8KB and 16KB

versions.

Table 11-2 shows reset and Interrupt Vectors placement for the various combinations of

BOOTRST and IVSEL settings. If the program never enables an interrupt source, the Interrupt

Vectors are not used, and regular program code can be placed at these locations. This is also

the case if the Reset Vector is in the Application section while the Interrupt Vectors are in the

Boot section or vice versa.

Note:

1. The Boot Reset Address is shown in Table 23-8 on page 239. For the BOOTRST Fuse “1”

means unprogrammed while “0” means programmed.

11.2.1

Moving Interrupts Between Application and Boot Space

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

11.3

11.3.1

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 “Memory Programming” on page 246 for

details. To avoid unintentional changes of Interrupt Vector tables, a special write procedure must

be followed to change the IVSEL bit:

$0034

ANALOG COMP

Analog Comparator

$0036

EE READY

EEPROM Ready

$0038

SPM READY

Store Program Memory Ready

Table 11-2.

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

Table 11-1.

Reset and Interrupt Vectors (Continued)

Vector

No.

Program

Address(2)

Source

Interrupt Definition

Bit

6543

210

0x35 (0x55)

JTD

–

PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

0000

000

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