Table 24-2. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0 Mode
BLB02
BLB01 Protection
1
2
1
1
1
0
No restrictions for SPM or LPM accessing the application section.
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.
3
0
0
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
Note:
1. “1” means unprogrammed, “0” means programmed.
Table 24-3. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1 Mode
BLB12
BLB11 Protection
1
2
1
1
1
0
No restrictions for SPM or LPM accessing the boot loader section.
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.
3
4
0
0
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” means unprogrammed, “0” means programmed
24.5 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 UART, 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
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.
Table 24-4. Boot Reset Fuse(1)
BOOTRST
Reset Address
1
0
Reset vector = Application reset (address 0x0000)
Reset vector = Boot loader Reset (see Table 24-7 on page 251)
Note:
1. “1” means unprogrammed, “0” means programmed
24.5.1 Store Program Memory Control and Status Register – SPMCSR
The store program memory control and status register contains the control bits needed to control the boot loader operations.
Bit
7
6
5
4
3
2
1
0
SPMEN
R/W
0
SPMIE RWWSB SIGRD RWWSRE BLBSET PGWRT PGERS
SPMCSR
Read/Write
Initial Value
R/W
0
R
0
R
0
R/W
0
R/W
0
R/W
0
R/W
0
244
ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
