ATMEGA8_08 Datasheet, PDF (223/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

Fuse Bits
ATmega8(L)
Table 86. Lock Bit Protection Modes⁽²⁾ (Continued)
Memory Lock Bits
Protection Type
1
1
1
No restrictions for SPM or LPM accessing the Boot Loader
section.
2
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
3
0
0
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.
LPM executing from the Application section is not allowed
4
0
1
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.
Notes: 1. Program the Fuse Bits before programming the Lock Bits.
2. “1” means unprogrammed, “0” means programmed
The ATmega8 has two fuse bytes. Table 87 and Table 88 describe briefly the functionality 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
RSTDISBL⁽⁴⁾
7
1 (unprogrammed, PC6 is
Select if PC6 is I/O pin or RESET pin RESET-pin)
WDTON
6
WDT always on
1 (unprogrammed, WDT
enabled by WDTCR)
SPIEN⁽¹⁾
CKOPT⁽²⁾
5
Enable Serial Program and Data
Downloading
4 Oscillator options
0 (programmed, SPI prog.
enabled)
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
BOOTSZ1
2
Select Boot Size (see Table 82 for
details)
0 (programmed)⁽³⁾
BOOTSZ0
1
Select Boot Size (see Table 82 for
details)
0 (programmed)⁽³⁾
BOOTRST
0 Select Reset Vector
1 (unprogrammed)
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 26 for details.
3. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 82 on page 220.
4. When programming the RSTDISBL Fuse Parallel Programming has to be used to change
fuses or perform further programming.
2486T–AVR–05/08
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