170
2588B–AVR–11/06
ATtiny261/461/861
Notes: 1. See ”System Clock Prescaler” on page 31 for details.
2. The CKOUT Fuse allows the system clock to be output on PORTB5. 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 28 for details.
4. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6
on page 28 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.
22.2.1 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.
22.3 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. The ATtiny261/461/861signature
bytes are given in Table 22-6.
22.4 Calibration Byte
Signature area of the ATtiny261/461/861 has one byte of calibration data for the internal RC
Oscillator. This byte resides in the high byte of address 0x000. During reset, this byte is auto-
matically written into the OSCCAL Register to ensure correct frequency of the calibrated RC
Oscillator.
Table 22-5. 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)
Table 22-6. Device ID
Parts
Signature Bytes Address
0x000 0x001 0x002
ATtiny261 0x1E 0x91 0x0C
ATtiny461 0x1E 0x92 0x08
ATtiny861 0x1E 0x93 0x0D
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