Datasheet

ManualsBrandsMicrochip ManualsAVR MicrocontrollersAVR RISC Microcontroller Flash 64KB TQFP

341

342

343

344

345

346

347

348

349

350

Table 27-2. Boot Reset Fuse

BOOTRST Reset Address

1 Reset Vector = Application Reset (address 0x0000)

0 Reset Vector = Boot Loader Reset, as described by the Boot Loader Parameters

Note: '1' means unprogrammed, '0' means programmed.

27.6. 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

The Boot 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

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.

Table 27-3. Boot Lock Bit0 Protection Modes (Application Section)

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.

3 0 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.

4 0 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.

Note: “1” means unprogrammed, “0” means programmed.

Table 27-4. Boot Lock Bit1 Protection Modes (Boot Loader Section)

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.

Atmel ATmega644A [DATASHEET]

Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016

349