277
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
Note:
2. The SPIEN Fuse is not accessible in serial programming mode.
.
Notes:
1. The default value of SUT1..0 results in maximum start-up time for the default clock source. See
Table 8-9 on page2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8MHz. See
Table 8-9 on page 31 for details.
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.
27.3.1
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.
Table 27-6.
Fuse High byte.
High Fuse byte
Bit no.
Description
Default value
7
External reset disable
1 (unprogrammed)
DWEN
6
debugWIRE enable
1 (unprogrammed)
5
Enable Serial Program and Data Downloading
0 (programmed, SPI
programming enabled)
4
Watchdog Timer always on
1 (unprogrammed)
EESAVE
3
EEPROM memory is preserved through the
Chip Erase
1 (unprogrammed),
EEPROM not reserved
BOOTSZ1
2
Select Boot Size (see Table 113 for details)
BOOTSZ0
1
Select Boot Size (see Table 113 for details)
BOOTRST
0
Select Reset Vector
1 (unprogrammed)
Table 27-7.
Fuse Low byte.
Low Fuse byte
Bit no.
Description
Default value
7
Divide clock by 8
0 (programmed)
6
Clock output
1 (unprogrammed)
SUT1
5
Select start-up time
SUT0
4
Select start-up time
CKSEL3
3
Select Clock source
CKSEL2
2
Select Clock source
CKSEL1
1
Select Clock source
CKSEL0
0
Select Clock source