ATtiny261-ESSZ datasheet(173/227 Pages) ATMEL

173 / 227 page

173

7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

Notes:

1. See “System Clock Prescaler” on page 32 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 29 for details.

4. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8.0 MHz. See Table 7-6

on page 29 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

Bit No

Description

Default Value

CKDIV8(1)

Divide clock by 8

0 (programmed)

CKOUT(2)

Clock Output Enable

1 (unprogrammed)

SUT1

Select start-up time

1 (unprogrammed)(3)

SUT0

Select start-up time

0 (programmed)(3)

CKSEL3

Select Clock source

0 (programmed)(4)

CKSEL2

Select Clock source

0 (programmed)(4)

CKSEL1

Select Clock source

1 (unprogrammed)(4)

CKSEL0

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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