Datasheet

346
7766E–AVR–04/10
ATmega16U4/ATmega32U4
28. Memory Programming
28.1 Program And Data Memory Lock Bits
The ATmega16U4/ATmega32U4 provides six Lock bits which can be left unprogrammed (“1”) or
can be programmed (“0”) to obtain the additional features listed in Table 28-2. The Lock bits can
only be erased to “1” with the Chip Erase command.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 28-1. Lock Bit Byte
(1)
Lock Bit Byte Bit No Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
BLB12 5 Boot Lock bit 1 (unprogrammed)
BLB11 4 Boot Lock bit 0 (programmed)
BLB02 3 Boot Lock bit 1 (unprogrammed)
BLB01 2 Boot Lock bit 1 (unprogrammed)
LB2 1 Lock bit 0 (programmed)
LB1 0 Lock bit 0 (programmed)
Table 28-2. Lock Bit Protection Modes
(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
210
Further programming of the Flash and EEPROM is
disabled in Parallel and Serial Programming mode. The
Fuse bits are locked in both Serial and Parallel
Programming mode.
(1)
300
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming
mode. The Boot Lock bits and Fuse bits are locked in both
Serial and Parallel Programming mode.
(1)
BLB0 Mode BLB02 BLB01
111
No restrictions for SPM or (E)LPM accessing the
Application section.
2 1 0 SPM is not allowed to write to the Application section.
300
SPM is not allowed to write to the Application section, and
(E)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.
401
(E)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.