Datasheet

237
7734Q–AVR–02/12
AT90PWM81/161
Note: 1. “1” means unprogrammed, “0” means programmed.
Note: 1. “1” means unprogrammed, “0” means programmed.
20.5 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 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 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 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 20-2. 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.
30 0
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.
40 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.
Table 20-3. 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.
30 0
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.
40 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.
Table 20-4. Boot reset fuse
(1)
.
BOOTRST Reset address
1 Reset vector = application reset (address 0x0000)
0 Reset vector = boot loader reset (see Table 20-7 on page 246)