Datasheet
151
2586D–AVR–02/06
ATtiny25/45/85
Notes: 1. See ”System Clock Prescaler” on page 30 for details.
2. The CKOUT Fuse allows the system clock to be output on PORTB4. See “Clock Output Buffer”
on page 30 for details.
3. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 7-7 on page 27 for details.
4. The default setting of CKSEL1..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6
on page 27 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.
23.2.1 Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of the
fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.
23.3 Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and High-voltage Programming mode, also when the device is
locked. The three bytes reside in a separate address space.
23.3.1 ATtiny25 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x91 (indicates 2 KB Flash memory).
3. 0x002: 0x08 (indicates ATtiny25 device when 0x001 is 0x91).
23.3.2 ATtiny45 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x92 (indicates 4 KB Flash memory).
3. 0x002: 0x06 (indicates ATtiny45 device when 0x001 is 0x92).
23.3.3 ATtiny85 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8 KB Flash memory).
3. 0x002: 0x0B (indicates ATtiny85 device when 0x001 is 0x93).
Table 23-5. Fuse Low Byte
Fuse Low Byte Bit No Description Default Value
CKDIV8
(1)
7 Divide clock by 8 0 (programmed)
CKOUT
(2)
6 Clock Output Enable 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)
(3)
SUT0 4 Select start-up time 0 (programmed)
(3)
CKSEL3 3 Select Clock source 0 (programmed)
(4)
CKSEL2 2 Select Clock source 0 (programmed)
(4)
CKSEL1 1 Select Clock source 1 (unprogrammed)
(4)
CKSEL0 0 Select Clock source 0 (programmed)
(4)