Datasheet

180
8246B–AVR–09/11
ATtiny2313A/4313
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 pro-
grammed before lock bits.
Fuse bits are not affected by a Chip Erase.
20.2.1 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.
20.3 Device Signature Imprint Table
The device signature imprint table is a dedicated read only memory area used for storing miscel-
laneous 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.
Notes: 1. See section “Signature Bytes” for more information.
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)
5SUT1
–
Sets system start-up time
Pages 28,
29, and 31
1 (unprogrammed)
4 SUT0 0 (programmed)
(2)
3 CKSEL3
Selects clock source Page 27
0 (programmed)
(3)
2 CKSEL2 0 (programmed)
(3)
1 CKSEL1 1 (unprogrammed)
(3)
0 CKSEL0 0 (programmed)
(3)
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