Table 86. Lock Bit Protection Modes(2) (Continued)
Memory Lock Bits
Protection Type
No restrictions for SPM or LPM accessing the Boot Loader
section.
1
2
1
1
1
0
SPM is not allowed to write to the Boot Loader section.
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader
section.
3
0
0
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
4
0
1
Notes: 1. Program the Fuse Bits before programming the Lock Bits.
2. “1” means unprogrammed, “0” means programmed
Fuse Bits
The ATmega8 has two fuse bytes. Table 87 and Table 88 describe briefly the functional-
ity of all the fuses and how they are mapped into the fuse bytes. Note that the fuses are
read as logical zero, “0”, if they are programmed.
Table 87. Fuse High Byte
Fuse High
Byte
Bit
No.
Description
Default Value
1 (unprogrammed, PC6 is
Select if PC6 is I/O pin or RESET pin RESET-pin)
RSTDISBL(4)
7
6
1 (unprogrammed, WDT
enabled by WDTCR)
WDTON
WDT always on
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
SPIEN(1)
CKOPT(2)
EESAVE
5
4
3
Oscillator options
1 (unprogrammed)
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
Select Boot Size (see Table 82 for
details)
BOOTSZ1
2
0 (programmed)(3)
Select Boot Size (see Table 82 for
details)
BOOTSZ0
BOOTRST
1
0
0 (programmed)(3)
1 (unprogrammed)
Select Reset Vector
Notes: 1. The SPIEN Fuse is not accessible in Serial Programming mode.
2. The CKOPT Fuse functionality depends on the setting of the CKSEL bits, see “Clock
Sources” on page 24 for details.
3. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 82 on
page 217.
4. When programming the RSTDISBL Fuse Parallel Programming has to be used to
change fuses or perform further programming.
220
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
