Datasheet
ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
254
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.
28.2.1 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.
28.3 Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial
and parallel mode, also when the device is locked. The three bytes reside in a separate address space. For the Atmel
®
ATmega48PA/88PA/168PA the signature bytes are given in Table 28-8.
28.4 Calibration Byte
The Atmel ATmega48PA/88PA/168PA has 2 calibration values for the Internal RC oscillator. The 3V calibration byte resides
in the address 0x0001 in the signature address space and the 5V calibration byte resides in the address 0x0009. During
reset, the 3V calibration byte is automatically written into the OSCCAL register to ensure correct frequency of the calibrated
RC oscillator.
Table 28-7. Fuse Low Byte
Low Fuse Byte Bit No Description Default Value
CKDIV8
(4)
7 Divide clock by 8 0 (programmed)
CKOUT
(3)
6 Clock output 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)
(1)
SUT0 4 Select start-up time 0 (programmed)
(1)
CKSEL3 3 Select clock source 0 (programmed)
(2)
CKSEL2 2 Select clock source 0 (programmed)
(2)
CKSEL1 1 Select clock source 1 (unprogrammed)
(2)
CKSEL0 0 Select clock source 0 (programmed)
(2)
Note: 1. The default value of SUT1...0 results in maximum start-up time for the default clock source. See Table 9-12 on
page 30 for details.
2. The default setting of CKSEL3...0 results in internal RC oscillator at 8MHz. See Table 9-11 on page 30 for
details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. See Section 9.9 “Clock Output Buffer” on
page 32 for details.
4. See Section 9.11 “System Clock Prescaler” on page 32 for details.
Table 28-8. Device ID
Part
Signature Bytes Address
0x000 0x002 0x004
Atmel ATmega48PA 0x1E 0x92 0x0A
Atmel ATmega88PA 0x1E 0x93 0x0F
Atmel ATmega168PA 0x1E 0x94 0x0B