25. Memory Programming
25.1 Program and Data Memory Lock Bits
The ATmega16/32/64/M1/C1 provides six Lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to
obtain the additional features listed in Table 25-2. The Lock bits can only be erased to “1” with the chip erase command.
Table 25-1. Lock Bit Byte(1)
Lock Bit Byte
Bit No
Description
–
Default Value
7
6
5
4
3
2
1
0
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
1 (unprogrammed)
–
BLB12
BLB11
BLB02
BLB01
LB2
Boot lock bit
Boot lock bit
Boot lock bit
Boot lock bit
Lock bit
LB1
Lock bit
Notes: 1. “1” means unprogrammed, “0” means programmed.
Table 25-2. Lock Bit Protection Modes(1)(2)
Memory Lock Bits
LB Mode
LB2
LB1
Protection Type
1
1
1
No memory lock features enabled.
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).
2
3
1
0
0
0
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).
Notes: 1. Program the fuse bits and boot lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed.
Table 25-3. Lock Bit Protection Modes(1)(2)
.
BLB0 Mode
BLB02
BLB01
1
2
1
1
1
0
No restrictions for SPM or LPM accessing the Application section.
SPM is not allowed to write to the Application section.
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.
3
4
0
0
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.
Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
ATmega16/32/64/M1/C1 [DATASHEET]
255
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
