209
ATmega8A [DATASHEET]
8159E–AVR–02/2013
Notes:
1. The default value of SUT1:0 results in maximum start-up time. See
Table 9-9 on page 29 for details.
2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 1MHz. See
Table 9-1 on page 25 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 pro-
grammed. Program the Fuse Bits before programming the Lock Bits.
25.2.1
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.
25.3
Signature Bytes
All Atmel microcontrollers have a 3-byte signature code which identifies the device. This code can be read in both
Serial and Parallel mode, also when the device is locked. The three bytes reside in a separate address space.
For the ATmega8A the signature bytes are:
1.
0x000: 0x1E (indicates manufactured by Atmel).
2.
0x001: 0x93 (indicates 8KB Flash memory).
3.
0x002: 0x07 (indicates ATmega8A device).
25.4
Calibration Byte
The ATmega8A stores four different calibration values for the internal RC Oscillator. These bytes resides in the sig-
nature row High byte of the addresses 0x0000, 0x0001, 0x0002, and 0x0003 for 1, 2, 4, and 8MHz respectively.
During Reset, the 1MHz value is automatically loaded into the OSCCAL Register. If other frequencies are used,
details.
Table 25-4.
Fuse Low Byte
Fuse Low
Byte
Bit No.
Description
Default Value
BODLEVEL
7
Brown out detector trigger level
1 (unprogrammed)
BODEN
6
Brown out detector enable
1 (unprogrammed, BOD disabled)
SUT1
5
Select start-up time
SUT0
4
Select start-up time
CKSEL3
3
Select Clock source
CKSEL2
2
Select Clock source
CKSEL1
1
Select Clock source
CKSEL0
0
Select Clock source