ATtiny261A datasheet(169/292 Pages) ATMEL

169 / 292 page

169

8197A–AVR–10/09

ATtiny261A/461A/861A

Notes: 1. See “System Clock Prescaler” on page 31 for details.

2. Allows system clock to be output on pin. See “Clock Output Buffer” on page 32 for details.

3. The default value results in maximum start-up time for the default clock source. See Table 6-7

on page 28 for details.

4. The default setting results in internal oscillator @ 8.0 MHz. See Table 6-6 on page 28 for

details.

Note that fuse bits are locked if Lock Bit 1 (LB1) is programmed. Fuse bits should be pro-

grammed before lock bits. The status of fuse bits is not affected by chip erase.

Fuse bits can also be read by device firmware. See section “Reading Fuse and Lock Bits from

Software” on page 164.

18.2.1

Latching of Fuses

Fuse values are latched when the device enters programming mode and changes to fuse values

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. Fuses are also latched on power-up.

18.3 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 signature bytes are given in

Table 18-6.

18.4 Calibration Byte

The signature area has one byte of calibration data for the internal oscillator. This byte resides in

the high byte of address 0x000. During reset, this byte is automatically written into the OSCCAL

Table 18-5.

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 18-6.

Device ID

Parts

Signature Bytes Address

0x000

0x001

0x002

ATtiny261A

0x1E

0x91

0x0C

ATtiny461A

0x1E

0x92

0x08

ATtiny861A

0x1E

0x93

0x0D

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