Datasheet
337
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
Notes: 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 29-7 on page 328
for details.
3. See “WDTCSR – Watchdog Timer Control Register” 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.
Notes: 1. The default value of SUT1:0 results in maximum start-up time for the default clock source. See
“System and Reset Characteristics” on page 372 for details.
2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 8 MHz. See Table 10-1 on
page 41 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Output Buffer”
on page 49 for details.
4. See “System Clock Prescaler” on page 49 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 30-4. 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 30-9 on
page 339 for details)
0 (programmed)
(2)
BOOTSZ0 1
Select Boot Size (see Table 30-9 on
page 339 for details)
0 (programmed)
(2)
BOOTRST 0 Select Reset Vector 1 (unprogrammed)
Table 30-5. 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)