ATMEGA165P Datasheet, PDF (261/365 Pages) ATMEL Corporation – 8-bit AVR Microcontroller with 16K Bytes In-System Programmable Flash

ATmega165P
24.4 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 different 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.
See Table 24-2 and Table 24-3 for further details. The Boot Lock bits and general Lock 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 pro-
gramming 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.
Table 24-2. 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.
SPM is not allowed to write to the Application section, and LPM
executing from the Boot Loader section is not allowed to read
3
0
0
from the Application section. If Interrupt Vectors are placed in
the Boot Loader section, interrupts are disabled while executing
from the Application section.
LPM executing from the Boot Loader section is not allowed to
4
0
1
read from the Application section. If Interrupt Vectors are placed
in the Boot Loader section, interrupts are disabled while
executing from the Application section.
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
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.
SPM is not allowed to write to the Boot Loader section, and LPM
executing from the Application section is not allowed to read
3
0
0
from the Boot Loader section. If Interrupt Vectors are placed in
the Application section, interrupts are disabled while executing
from the Boot Loader section.
LPM executing from the Application section is not allowed to
4
0
1
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. “1” means unprogrammed, “0” means programmed
8018A–AVR–03/06
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