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Table 20-5. Low Fuse Byte

Bit #

Bit Name

Use

See

Default Value

 

 

 

 

 

 

7

CKDIV8

Divides clock by 8 (1)

Page 28

0

(programmed)

6

CKOUT

Outputs system clock on port pin

Page 32

1

(unprogrammed)

 

 

 

 

 

 

5

SUT1

Pages 28,

1

(unprogrammed)

4

SUT0

Sets system start-up time

29, and 31

0

(programmed) (2)

3

CKSEL3

 

 

0

(programmed) (3)

2

CKSEL2

Selects clock source

Page 27

0

(programmed) (3)

1

CKSEL1

1

(unprogrammed) (3)

 

 

0

CKSEL0

 

 

0

(programmed) (3)

Note:

1. Unprogramming this fuse at low voltages may result in overclocking. See Section 22.3 on page

 

200 for device speed versus supply voltage.

 

 

 

2.This setting results in maximum start-up time for the default clock source.

3.This setting selects Calibrated Internal RC Oscillator.

Fuse bits are locked when Lock Bit 1 (LB1) is programmed. Hence, fuse bits must be programmed before lock bits.

Fuse bits are not affected by a Chip Erase.

20.2.1Latching 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.

20.3Device Signature Imprint Table

The device signature imprint table is a dedicated read only memory area used for storing miscellaneous device information, such as the device signature and oscillator calibration data. Most of this memory segment is reserved for internal use, as outlined in Table 20-6.

Byte addresses are used when the device itself reads the data with the LPM command. External programming devices must use word addresses.

Table 20-6. Contents of Device Signature Imprint Table.

Word Address

Byte Address

High Byte

 

 

 

0x00

0x00

Signature byte 0 (1)

0x01

Calibration data for internal 8 MHz oscillator (2)

 

0x01

0x02

Signature byte 1 (1)

0x03

Calibration data for internal 4 MHz oscillator (2)

 

0x02

0x04

Signature byte 2 (1)

0x05 ...

Reserved for internal use

 

 

 

 

Notes: 1. See section “Signature Bytes” for more information.

180 ATtiny2313A/4313

8246B–AVR–09/11

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