Table 29-4. Fuse High Byte
Fuse High Byte Bit No Description
Default Value
1 (unprogrammed, OCD
disabled)
OCDEN(4)
7
6
Enable OCD
Enable JTAG
0 (programmed, JTAG
enabled)
JTAGEN
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 29-6
for details)
BOOTSZ1
2
0 (programmed)(2)
Select Boot Size (see Table 29-6
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 28-8 on page 366
for details.
3. See “Watchdog Timer Control Register - WDTCSR” 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.
Table 29-5. 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 8-1 on page 59 for details.
2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See Table 6-1 on
page 39 for details.
3. The CKOUT Fuse allow the system clock to be output on PORTC7. See “Clock Output Buffer”
on page 47 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.
370
AT90USB64/128
7593A–AVR–02/06
ATMEL [ ATMEL ]
