Datasheet

150
2586D–AVR–02/06
ATtiny25/45/85
23.2 Fuse Bytes
The ATtiny25/45/85 has three Fuse bytes. Table 23-4, Table 23-5 and Table61 describe briefly
the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the
fuses are read as logical zero, “0”, if they are programmed.
Notes: 1. See ”Alternate Functions of Port B” on page 59 for description of RSTDISBL and DWEN
Fuses.
2. DWEN must be unprogrammed when Lock Bit security is required. See Section “23.1” on page
149.
3. The SPIEN Fuse is not accessible in SPI Programming mode.
4. See ”WDTCR – Watchdog Timer Control Register” on page 42 for details.
5. See Table 9-2 on page 38 for BODLEVEL Fuse decoding.
6. When programming the RSTDISBL Fuse, High-voltage Serial programming has to be used to
change fuses to perform further programming.
Table 23-3. Fuse Extended Byte
Fuse High Byte Bit No Description Default Value
7 - 1 (unprogrammed)
6 - 1 (unprogrammed)
5 - 1 (unprogrammed)
4 - 1 (unprogrammed)
3 - 1 (unprogrammed)
2 - 1 (unprogrammed)
1 - 1 (unprogrammed)
SELFPRGEN 0 Self-Programming Enable 1 (unprogrammed)
Table 23-4. Fuse High Byte
Fuse High Byte Bit No Description Default Value
RSTDISBL
(1)
7 External Reset disable 1 (unprogrammed)
DWEN
(2)
6 DebugWIRE Enable 1 (unprogrammed)
SPIEN
(3)
6
Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
WDTON
(4)
4 Watchdog Timer always on 1 (unprogrammed)
EESAVE 3
EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed, EEPROM
not preserved)
BODLEVEL2
(5)
2 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL1
(5)
1 Brown-out Detector trigger level 1 (unprogrammed)
BODLEVEL0
(5)
0 Brown-out Detector trigger level 1 (unprogrammed)