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ATmega165A/PA/325A/PA/3250A/PA/645A/P/6450A/P [DATASHEET]
8285E–AVR–02/2013
26.5
Boot Loader Lock Bits
If no Boot Loader capability is needed, the entire Flash is available for application code. The Boot Loader has two
separate sets of Boot Lock bits which can be set independently. This gives the user a unique flexibility to select dif-
ferent levels of protection.
The user can select:
To protect the entire Flash from a software update by the MCU
To protect only the Boot Loader Flash section from a software update by the MCU
To protect only the Application Flash section from a software update by the MCU
Allow software update in the entire Flash
bits can be set in software and in Serial or Parallel Programming mode, but they can be cleared by a Chip Erase
command only. The general Write Lock (Lock Bit mode 2) does not control the programming of the Flash memory
by SPM instruction. Similarly, the general Read/Write Lock (Lock Bit mode 1) does not control reading nor writing
by LPM/SPM, if it is attempted.
Note:
1. “1” means unprogrammed, “0” means programmed
.
Note:
1. “1” means unprogrammed, “0” means programmed.
Table 26-2.
Boot Lock Bit0 Protection modes (Application section)
(1).BLB0 Mode
BLB02
BLB01
Protection
11
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 26-3.
Boot Lock Bit1 Protection modes (Boot Loader section)
(1).
BLB1 Mode
BLB12
BLB11
Protection
11
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.