4 boot loader lock bits, Figure 27-2 – Rainbow Electronics ATmega64M1 User Manual
Page 275
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8209A–AVR–08/09
ATmega16M1/32M1/64M1
Figure 27-2. Memory Sections
Note:
1. The parameters in the figure above are given in
27.4
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.
for further details. 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.
0x0000
Flashend
Program Memory
BOOTSZ = '11'
Application Flash Section
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '10'
0x0000
Program Memory
BOOTSZ = '01'
Program Memory
BOOTSZ = '00'
Application Flash Section
Boot Loader Flash Section
0x0000
Flashend
Application Flash Section
Flashend
End RWW
Start NRWW
Application Flash Section
Boot Loader Flash Section
Boot Loader Flash Section
End RWW
Start NRWW
End RWW
Start NRWW
0x0000
End RWW, End Application
Start NRWW, Start Boot Loader
Application Flash Section
Application Flash Section
Application Flash Section
Read-While-Wr
ite
S
ection
No Read-While-Wr
ite
S
ection
Read-While-Wr
ite
S
ection
No Read-While-Wr
ite
S
ection
Read-While-Wr
ite
S
ection
No Read-While-Wr
ite
S
ection
Read-While-Wr
ite
S
ection
No Read-While-Wr
ite
S
ection
End Application
Start Boot Loader
End Application
Start Boot Loader
End Application
Start Boot Loader