ATmega640/1280/1281/2560/2561
Table 151. Fuse High Byte
Fuse High Byte Bit No Description
Default Value
1 (unprogrammed, OCD
disabled)
OCDEN(4)
7
6
Enable OCD
0 (programmed, JTAG
enabled)
JTAGEN
Enable JTAG
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
SPIEN(1)
WDTON(3)
EESAVE
5
4
3
Watchdog Timer always on
1 (unprogrammed)
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
Select Boot Size (see Table 153
for details)
BOOTSZ1
2
0 (programmed)(2)
Select Boot Size (see Table 153
for details)
BOOTSZ0
BOOTRST
1
0
0 (programmed)(2)
1 (unprogrammed)
Select Reset Vector
Note:
1. The SPIEN Fuse is not accessible in serial programming mode.
2. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 139 on
page 330 for details.
3. See “Watchdog Timer Control Register - WDTCSR” on page 67 for details.
4. Never ship a product with the OCDEN Fuse programmed regardless of the setting of
Lock bits and JTAGEN Fuse. A programmed OCDEN Fuse enables some parts of the
clock system to be running in all sleep modes. This may increase the power
consumption.
Table 152. Fuse Low Byte
Fuse Low Byte
CKDIV8(4)
CKOUT(3)
SUT1
Bit No
Description
Default Value
7
6
5
4
3
2
1
0
Divide clock by 8
Clock output
0 (programmed)
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
Note:
1. The default value of SUT1..0 results in maximum start-up time for the default clock
source. See Table 23 on page 58 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See
Table 7 on page 40 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Out-
put Buffer” on page 48 for details.
4. See “System Clock Prescaler” on page 48 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.
337
2549A–AVR–03/05
ATMEL [ ATMEL ]
