Datasheet

29. MEMPROG- Memory Programming
29.1 Program and Data Memory Lock Bits
The ATmega8A provides six Lock bits. These can be left unprogrammed ('1') or can be programmed ('0')
to obtain the additional features listed in the Lock Bit Protection Modes table below. The Lock Bits can
only be erased to “1” with the Chip Erase command.
Table 29-1. 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)
Note: 1. “1” means unprogrammed, “0” means programmed.
Table 29-2. 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 Load Program Memory (LPM) instruction
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
AVR 8-Bit Microcontroller
MEMPROG- Memory Programming
© 2017 Microchip Technology Inc.
Datasheet Complete
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