Data Sheet
285
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
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 @ 8MHz. 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 ATmega48A/PA/88A/PA/168A/PA/328/P the signature bytes are given in Table 28-10.
28.4 Calibration Byte
The ATmega48A/PA/88A/PA/168A/PA/328/P 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.
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 28-9. Fuse Low Byte (Continued)
Low Fuse Byte Bit No Description Default Value
Table 28-10. Device ID
Part
Signature Bytes Address
0x000 0x001 0x002
ATmega48A 0x1E 0x92 0x05
ATmega48PA 0x1E 0x92 0x0A
ATmega88A 0x1E 0x93 0x0A
ATmega88PA 0x1E 0x93 0x0F
ATmega168A 0x1E 0x94 0x06
ATmega168PA 0x1E 0x94 0x0B
ATmega328 0x1E 0x95 0x14
ATmega328P 0x1E 0x95 0x0F