ATmega48/88/168
Table 105. 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
3
1
0
0
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 from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
4
0
1
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.
Note:
1. “1” means unprogrammed, “0” means programmed
Table 106. 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
3
1
0
0
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 from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
4
0
1
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.
Note:
1. “1” means unprogrammed, “0” means programmed
Entering the Boot Loader 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-
Program
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 107. Boot Reset Fuse(1)
BOOTRST
Reset Address
1
0
Reset Vector = Application Reset (address 0x0000)
Reset Vector = Boot Loader Reset (see Table 109 on page 268)
Note:
1. “1” means unprogrammed, “0” means programmed
259
2545D–AVR–07/04
ATMEL [ ATMEL ]
