Datasheet

294
8025M–AVR–6/11
ATmega48P/88P/168P
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 34 for details.
2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 8 MHz. See Table 9-11 on
page 34 for details.
3. The CKOUT Fuse allows the system clock to be output on PORTB0. See ”Clock Output Buffer”
on page 36 for details.
4. See ”System Clock Prescaler” on page 36 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 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 ATmega48P/88P/168P the signature bytes
are given in Table 28-8.
28.4 Calibration Byte
The ATmega48P/88P/168P has a byte calibration value for the Internal RC Oscillator. This byte
resides in the high byte of address 0x000 in the signature address space. During reset, this 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)
Table 28-8. Device ID
Part
Signature Bytes Address
0x000 0x001 0x002
ATmega48P 0x1E 0x92 0x0A
ATmega88P 0x1E 0x93 0x0F
ATmega168P 0x1E 0x94 0x0B