Datasheet
344
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
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 140 on
page 335 for details.
3. See “WDTCSR – Watchdog Timer Control Register” on page 66 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.
Note: 1. The default value of SUT1:0 results in maximum start-up time for the default clock
source. See Table 26 on page 58 for details.
2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 8 MHz. See
Table 10 on page 39 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Out-
put Buffer” on page 46 for details.
4. See “System Clock Prescaler” on page 47 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.
Table 152. Fuse High Byte
Fuse High Byte Bit No Description Default Value
OCDEN
(4)
7
Enable OCD
1 (unprogrammed, OCD
disabled)
JTAGEN 6
Enable JTAG
0 (programmed, JTAG
enabled)
SPIEN
(1)
5
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
WDTON
(3)
4 Watchdog Timer always on 1 (unprogrammed)
EESAVE 3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
BOOTSZ1 2
Select Boot Size (see Table 157
for details) 0 (programmed)
(2)
BOOTSZ0 1
Select Boot Size (see Table 157
for details) 0 (programmed)
(2)
BOOTRST 0 Select Reset Vector 1 (unprogrammed)
Table 153. Fuse Low Byte
Fuse Low 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)