Boot Lock Bit0 Protection Modes (Application Section); Boot Lock Bit1 Protection Modes (Boot Loader Section); Boot Reset Fuse - Atmel ATmega128 Manual

Entering the Boot
Loader Program
ATmega128
276
Table 108. Boot Lock Bit0 Protection Modes (Application Section)
BLB0 mode BLB02
1 1
2 1
3 0
4 0
Note: 1. "1" means unprogrammed, "0" means programmed
Table 109. Boot Lock Bit1 Protection Modes (Boot Loader Section)
BLB1 mode BLB12
1 1
2 1
3 0
4 0
Note: 1. "1" means unprogrammed, "0´means programmed
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 Reset 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.
Table 110. Boot Reset Fuse
BOOTRST Reset Address
1 Reset Vector = Application Reset (address $0000)
0 Reset Vector = Boot Loader Reset (see
Note: 1. "1" means unprogrammed, "0´means programmed
BLB01 Protection
No restrictions for SPM or LPM accessing the Application
1
section.
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
0 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
1
vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
BLB1
1 Protection
No restrictions for SPM or LPM accessing the Boot Loader
1
section.
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
0 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
1
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
(1)
(1)
(1)
Table 112 on page 284)
2467S–AVR–07/09