135
7598H–AVR–07/09
ATtiny25/45/85
Notes: 1. Program the Fuse bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
21.2 Fuse Bytes
The ATtiny25/45/85 has three Fuse bytes. Table 21-4, Table 21-5 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.
Table 21-2. Lock Bit Protection Modes
(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
210
Further programming of the Flash and EEPROM is disabled in
High-voltage and Serial Programming mode. The Fuse bits are
locked in both Serial and High-voltage Programming mode.
(1)
debugWire is disabled.
300
Further programming and verification of the Flash and
EEPROM is disabled in High-voltage and Serial Programming
mode. The Fuse bits are locked in both Serial and High-voltage
Programming mode.
(1)
debugWire is disabled.
Table 21-3. 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 21-4. 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)
5
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)
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