ATmega16 datasheet(244/315 Pages) ATMEL

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244

ATmega16(L)

2466E–AVR–10/02

Note:

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

Note:

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

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 inter-

face. 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 execut-

ing the application code. Note that the fuses cannot be changed by the MCU itself. This

means that once the Boot Reset Fuse is programmed, 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.

Table 95. 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 96. 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.

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