Table 30-10. BS2 and BS1 Encoding
Flash Data
Loading /
Reading
Flash / EEPROM
Fuse
Programming
Reading Fuse
and Lock Bits
BS2
0
BS1
0
Address
Low Byte
High Byte
Low Byte
High Byte
Low Byte
High Byte
Fuse Low Byte
Lockbits
0
1
Extended High
Byte
Extended Fuse
Byte
1
1
0
1
Reserved
Reserved
Extended Byte
Reserved
Reserved
Fuse High Byte
,
Table 30-11. Pin Values Used to Enter Programming Mode
Pin
PAGEL
XA1
Symbol
Value
Prog_enable[3]
Prog_enable[2]
Prog_enable[1]
Prog_enable[0]
0
0
0
0
XA0
BS1
Table 30-12. XA1 and XA0 Enoding
XA1
XA0
Action when XTAL1 is Pulsed
0
0
Load Flash or EEPROM Address (High or low address byte determined
by BS2 and BS1).
0
1
1
1
0
1
Load Data (High or Low data byte for Flash determined by BS1).
Load Command
No Action, Idle
Table 30-13. Command Byte Bit Encoding
Command Byte
1000 0000
0100 0000
0010 0000
0001 0000
0001 0001
0000 1000
0000 0100
0000 0010
0000 0011
Command Executed
Chip Erase
Write Fuse bits
Write Lock bits
Write Flash
Write EEPROM
Read Signature Bytes and Calibration byte
Read Fuse and Lock bits
Read Flash
Read EEPROM
342
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
