ATmega328P datasheet(281/448 Pages) ATMEL

281 / 448 page

281

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

Note:

1. “1” means unprogrammed, “0” means programmed

Note:

1. “1” means unprogrammed, “0” means programmed

26.6

Entering the Boot Loader Program

Entering the Boot Loader takes place by a jump or call from the application program. This may

be initiated by a trigger such as a command received via USART, or SPI interface. Alternatively,

the Boot Reset Fuse can be programmed so that the Reset Vector is pointing to the Boot Flash

start address after a reset. In this case, the Boot Loader is started after a reset. After the applica-

tion code is loaded, the program can start executing the application code. Note that the fuses

cannot be changed by the MCU itself. This means that once the Boot Reset Fuse is pro-

grammed, the Reset Vector will always point to the Boot Loader Reset and the fuse can only be

changed through the serial or parallel programming interface.

Note:

1. “1” means unprogrammed, “0” means programmed

Table 26-2.

Boot Lock Bit0 Protection Modes (Application Section)(1)

BLB0 Mode

BLB02

BLB01

Protection

No restrictions for SPM or LPM accessing the Application

section.

SPM is not allowed to write to the Application section.

SPM is not allowed to write to the Application section, and LPM

executing from the Boot Loader section is not allowed to read

from the Application section. If Interrupt Vectors are placed in

the Boot Loader section, interrupts are disabled while executing

from the Application section.

LPM executing from the Boot Loader section is not allowed to

read from the Application section. If Interrupt Vectors are placed

in the Boot Loader section, interrupts are disabled while

executing from the Application section.

Table 26-3.

Boot Lock Bit1 Protection Modes (Boot Loader Section)

(1)

BLB1 Mode

BLB12

BLB11

Protection

No restrictions for SPM or LPM accessing the Boot Loader

section.

SPM is not allowed to write to the Boot Loader section.

SPM is not allowed to write to the Boot Loader section, and LPM

executing from the Application section is not allowed to read

from the Boot Loader section. If Interrupt Vectors are placed in

the Application section, interrupts are disabled while executing

from the Boot Loader section.

LPM executing from the Application section is not allowed to

read from the Boot Loader section. If Interrupt Vectors are

placed in the Application section, interrupts are disabled while

executing from the Boot Loader section.

Table 26-4.

Boot Reset Fuse

(1)

BOOTRST

Reset Address

Reset Vector = Application Reset (address 0x0000)

Reset Vector = Boot Loader Reset (see Table 26-7 on page 289)

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