Datasheet

219
ATmega8(L)
2486M–AVR–12/03
Memory
Programming
Program And Data
Memory Lock Bits
The ATmega8 provides six Lock Bits which can be left unprogrammed (“1”) or can be
programmed (“0”) to obtain the additional features listed in Table 86. The Lock Bits can
only be erased to “1” with the Chip Erase command.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 85. Lock Bit Byte
Lock Bit Byte Bit No. Description Default Value
(1)
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
BLB12 5 Boot lock bit 1 (unprogrammed)
BLB11 4 Boot lock bit 1 (unprogrammed)
BLB02 3 Boot lock bit 1 (unprogrammed)
BLB01 2 Boot lock bit 1 (unprogrammed)
LB2 1 Lock bit 1 (unprogrammed)
LB1 0 Lock bit 1 (unprogrammed)
Table 86. Lock Bit Protection Modes
(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
2 1 0
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)
3 0 0
Further programming and verification of the Flash and
EEPROM is disabled in parallel and Serial Programming
mode. The Fuse Bits are locked in both Serial and Parallel
Programming modes.
(1)
BLB0 Mode BLB02 BLB01
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.
BLB1 Mode BLB12 BLB11