ATMEGA640 datasheet(313/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Note:

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

Note:

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

29.4.1

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 trig-

ger 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 application 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 29-2.

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

BLB0 Mode

BLB02

BLB01

Protection

No restrictions for SPM or (E)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 (E)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.

(E)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 29-3.

Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)

BLB1 Mode

BLB12

BLB11

Protection

No restrictions for SPM or (E)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 (E)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.

(E)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 29-4.

Boot Reset Fuse(1)

BOOTRST

Reset Address

Reset Vector = Application Reset (address 0x0000)

Reset Vector = Boot Loader Reset (see Table 29-7 on page 320)

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