ATMega chip full datasheet - UCSD Department of Physics

ATmega48A/PA/88A/PA/168A/PA/328/PFigure 27-2.Memory SectionsProgram MemoryBOOTSZ = '11'0x0000Program MemoryBOOTSZ = '10'0x0000No Read-While-Write Section Read-While-Write SectionNo Read-While-Write Section Read-While-Write SectionApplication Flash SectionApplication Flash SectionBoot Loader Flash SectionProgram MemoryBOOTSZ = '01'Application Flash SectionApplication Flash SectionBoot Loader Flash SectionEnd RWWStart NRWWEnd ApplicationStart Boot LoaderFlashend0x0000End RWWStart NRWWEnd ApplicationStart Boot LoaderFlashendNo Read-While-Write Section Read-While-Write SectionNo Read-While-Write Section Read-While-Write SectionApplication Flash SectionApplication Flash SectionBoot Loader Flash SectionProgram MemoryBOOTSZ = '00'Application Flash SectionBoot Loader Flash SectionEnd RWWStart NRWWEnd ApplicationStart Boot LoaderFlashend0x0000End RWW, End ApplicationStart NRWW, Start Boot LoaderFlashendNote: 1. The parameters in the figure above are given in Table 27-7 on page 292.27.5 Boot Loader Lock BitsIf no Boot Loader capability is needed, the entire Flash is available for application code. TheBoot Loader has two separate sets of Boot Lock bits which can be set independently. This givesthe 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 27-2 and Table 27-3 for further details. The Boot Lock bits can be set in software andin Serial or Parallel Programming mode, but they can be cleared by a Chip Erase commandonly. The general Write Lock (Lock Bit mode 2) does not control the programming of the Flashmemory by SPM instruction. Similarly, the general Read/Write Lock (Lock Bit mode 1) does notcontrol reading nor writing by LPM/SPM, if it is attempted.8271D–AVR–05/11283