30.2.1
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.
30.3 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 ATmega640/1280/1281/2560/2561 the signa-
ture bytes are given in Table 30-6.
Table 30-6. Device and JTAG ID
Signature Bytes Address
JTAG
Part
0x000
0x001
0x96
0x97
0x97
0x98
0x98
0x002
Part Number
9608
Manufacture ID
0x1F
ATmega640
ATmega1280
ATmega1281
ATmega2560
ATmega2561
0x1E
0x1E
0x1E
0x1E
0x1E
0x08
0x03
0x04
0x01
0x02
9703
0x1F
9704
0x1F
9801
0x1F
9802
0x1F
30.4 Calibration Byte
The ATmega640/1280/1281/2560/2561 has a byte calibration value for the internal RC Oscilla-
tor. 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.
30.5 Page Size
Table 30-7. No. of Words in a Page and No. of Pages in the Flash
No. of
Flash Size
Page Size
PCWORD
Pages
PCPAGE
PCMSB
128K words (256K bytes)
128 words
PC[6:0]
1024
PC[16:7]
16
Table 30-8. No. of Words in a Page and No. of Pages in the EEPROM
No. of
EEPROM Size
Page Size
PCWORD
Pages
PCPAGE
EEAMSB
4K bytes
8 bytes
EEA[2:0]
512
EEA[11:3]
11
30.6 Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the ATmega640/1280/1281/2560/2561.
Pulses are assumed to be at least 250 ns unless otherwise noted.
340
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
