Datasheet

327
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
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.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 135. Boot Lock Bit0 Protection Modes (Application Section)
(1)
BLB0 Mode BLB02 BLB01 Protection
111No restrictions for SPM or (E)LPM accessing the
Application section.
2 1 0 SPM is not allowed to write to the Application section.
3 0 0 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.
4 0 1 (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 136. Boot Lock Bit1 Protection Modes (Boot Loader Section)
(1)
BLB1 Mode BLB12 BLB11 Protection
111No restrictions for SPM or (E)LPM accessing the Boot
Loader section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
3 0 0 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.
4 0 1 (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 137. Boot Reset Fuse
(1)
BOOTRST Reset Address
1 Reset Vector = Application Reset (address 0x0000)
0 Reset Vector = Boot Loader Reset (see Table 140 on page 335)