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286
2545T–AVR–05/11
ATmega48/88/168
Notes: 1. Program the fuse bits and boot lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed.
28.2 Fuse bits
The Atmel ATmega48/88/168 has three fuse bytes. Table 28-4 through Table 28-7 on page 288
describe briefly the functionality of all the fuses and how they are mapped into the fuse bytes.
Note that the fuses are read as logical zero, “0”, if they are programmed.
Table 28-3. Lock bit protection modes
(1)(2)
. Only Atmel ATmega88/168.
BLB0 mode BLB02 BLB01
111
No restrictions for SPM or LPM accessing the application
section.
2 1 0 SPM is not allowed to write to the application section.
300
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.
401
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.
BLB1 mode BLB12 BLB11
111
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.
300
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.
401
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 28-4. Extended fuse byte for mega48.
Extended fuse byte Bit no. Description Default value
–7– 1
–6– 1
–5– 1
–4– 1
–3– 1
–2– 1
–1– 1
SELFPRGEN 0 Self programming enable 1 (unprogrammed)