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.
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.
ATmega48 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x92 (indicates 4KB Flash memory).
3. 0x002: 0x05 (indicates ATmega48 device when 0x001 is 0x92).
ATmega88 Signature Bytes
ATmega168 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8KB Flash memory).
3. 0x002: 0x0A (indicates ATmega88 device when 0x001 is 0x93).
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB Flash memory).
3. 0x002: 0x06 (indicates ATmega168 device when 0x001 is 0x94).
Calibration Byte
Page Size
The ATmega48/88/168 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 fre-
quency of the calibrated RC Oscillator.
Table 122. No. of Words in a Page and No. of Pages in the Flash
Flash
Size
Page
Size
No. of
Pages
Device
PCWORD
PCPAGE
PCMSB
2K words
(4K bytes)
ATmega48
32 words
32 words
64 words
PC[4:0]
64
PC[10:5]
10
4K words
(8K bytes)
ATmega88
PC[4:0]
PC[5:0]
128
128
PC[11:5]
PC[12:6]
11
12
8K words
(16K bytes)
ATmega168
Table 123. No. of Words in a Page and No. of Pages in the EEPROM
EEPROM
Size
Page
Size
No. of
Pages
Device
PCWORD
EEA[1:0]
EEA[1:0]
EEA[1:0]
PCPAGE
EEA[7:2]
EEA[8:2]
EEA[8:2]
EEAMSB
ATmega48
ATmega88
ATmega168
256 bytes
512 bytes
512 bytes
4 bytes
4 bytes
4 bytes
64
7
8
8
128
128
274
ATmega48/88/168
2545D–AVR–07/04
ATMEL [ ATMEL ]
