Datasheet
High Fuse Byte Bit No. Description Default Value
EESAVE 3 EEPROM memory is preserved through
the Chip Erase
1 (unprogrammed), EEPROM not
reserved
BODLEVEL2
(4)
2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL1
(4)
1 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0
(4)
0 Brown-out Detector trigger level 1 (unprogrammed)
Note:
1. Please refer to Alternate Functions of Port C in I/O-Ports chapter for description of RSTDISBL
Fuse.
2. The SPIEN Fuse is not accessible in serial programming mode.
3. Please refer to WDTCSR – Watchdog Timer Control Register for details.
4. Please refer to Table BODLEVEL Fuse Coding in System and Reset Characteristics for BODLEVEL
Fuse decoding.
Table 28-8. Fuse Low Byte (0x62)
Low Fuse Byte Bit No. Description Default Value
CKDIV8
(4)
7 Divide clock by 8 0 (programmed)
CKOUT
(3)
6 Clock output 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)
(1)
SUT0 4 Select start-up time 0 (programmed)
(1)
CKSEL3 3 Select Clock source 0 (programmed)
(2)
CKSEL2 2 Select Clock source 0 (programmed)
(2)
CKSEL1 1 Select Clock source 1 (unprogrammed)
(2)
CKSEL0 0 Select Clock source 0 (programmed)
(2)
Note:
1. The default value of SUT[1:0] results in maximum start-up time for the default clock source. See
Table. Start-up times for the internal calibrated RC Oscillator clock selection in Calibrated Internal
RC Oscillator of System Clock and Clock Options chapter for details.
2. The default setting of CKSEL[3:0] results in internal RC Oscillator @ 8MHz. See Table 'Internal
Calibrated RC Oscillator Operating Modes' in Calibrated Internal RC Oscillator of the System Clock
and Clock Options chapter for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. Please refer to Clock Output
Buffer section in the System Clock and Clock Options chapter for details.
4. Please refer to System Clock Prescaler section in the System Clock and Clock Options chapter for
details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if Lock bit1
(LB1) is programmed. Program the Fuse bits before programming the Lock bits.
Related Links
Alternate Port Functions on page 99
Calibrated Internal RC Oscillator on page 48
Atmel ATmega644A [DATASHEET]
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