Table 25-6. Fuse High Byte
High Fuse Byte
RSTDISBL(1)
DWEN
Bit No
Description
Default Value
1 (unprogrammed)
1 (unprogrammed)
7
6
External reset disable
debugWIRE enable
Enable serial program and data
downloading
0 (programmed, SPI programming
enabled)
SPIEN(2)
WDTON(3)
EESAVE
5
4
3
Watchdog timer always on
1 (unprogrammed)
EEPROM memory is preserved
through the chip erase
1 (unprogrammed), EEPROM not
reserved
BOOTSZ1
BOOTSZ0
BOOTRST
2
1
0
Select boot size
Select boot size
Select reset vector
0 (programmed)(4)
0 (programmed)(4)
1 (unprogrammed)
Note:
1. See Section 9.3.3 “Alternate Functions of Port C” on page 61 for description of RSTDISBL fuse.
2. The SPIEN fuse is not accessible in serial programming mode.
3. See Section 7-5 “Watchdog Timer Configuration” on page 46 for details.
4. The default value of BOOTSZ1..0 results in maximum boot size. See Table 25-8 on page 259 for details.
Table 25-7. Fuse Low Byte
Low Fuse Byte
CKDIV8(4)
CKOUT(3)
SUT1
Bit No
Description
Default Value
0 (programmed)
7
6
5
4
3
2
1
0
Divide clock by 8
Clock output
1 (unprogrammed)
1 (unprogrammed)(1)
0 (programmed)(1)
0 (programmed)(2)
0 (programmed)(2)
1 (unprogrammed)(2)
0 (programmed)(2)
Select start-up time
Select start-up time
Select Clock source
Select Clock source
Select Clock source
Select Clock source
SUT0
CKSEL3
CKSEL2
CKSEL1
CKSEL0
Notes: 1. The default value of SUT1..0 results in maximum start-up time for the default clock source. See Table 5-9 on
page 32 for details.
2. The default setting of CKSEL3..0 results in internal RC oscillator at 8MHz. See Table 5-9 on page 32 for
details.
3. The CKOUT fuse allows the system clock to be output on PORTB0. See Section 5.9 “Clock Output Buffer” on
page 32 for details.
4. See Section 5.10 “System Clock Prescaler” on page 32 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.
25.3.1 Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect
until the part leaves programming mode. This does not apply to the EESAVE fuse which will take effect once it is
programmed. The fuses are also latched on power-up in normal mode.
ATmega16/32/64/M1/C1 [DATASHEET]
257
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
