ATMEGA8_08 Datasheet, PDF (212/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

Table 78. Boot Lock Bit0 Protection Modes (Application Section)⁽¹⁾
BLB0
Mode BLB02 BLB01 Protection
1
1
1
No restrictions for SPM or LPM accessing the Application
section.
2
1
0
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
3
0
0
from the Application section. If Interrupt Vectors are placed in
the Boot Loader section, interrupts are disabled while executing
from the Application section.
4
Note:
LPM executing from the Boot Loader section is not allowed to
0
1
read from the Application section. If Interrupt Vectors are placed
in the Boot Loader section, interrupts are disabled while
executing from the Application section.
1. “1” means unprogrammed, “0” means programmed
Table 79. Boot Lock Bit1 Protection Modes (Boot Loader Section)⁽¹⁾
BLB1
Mode BLB12 BLB11 Protection
1
1
1
No restrictions for SPM or LPM accessing the Boot Loader
section.
2
1
0
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
3
0
0
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
4
0
1
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.
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 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.
212 ATmega8(L)
2486T–AVR–05/08