ATmega169P datasheet(283/393 Pages) ATMEL

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8018N–AVR–08/09

ATmega169P

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 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 26-2 and Table 26-3 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.

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

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.

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

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.

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.

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