Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” on page 341 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is pro-
grammed (LB1 and LB2 is programmed), it is not possible to program the Boot
Lock bits by any External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
Reading the Fuse and Lock
Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming
the Flash” on page 341 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, and BS2, BS1 to “00”. The status of the Fuse Low bits can now be
read at DATA (“0” means programmed).
3. Set OE to “0”, and BS2, BS1 to “11”. The status of the Fuse High bits can now be
read at DATA (“0” means programmed).
4. Set OE to “0”, and BS2, BS1 to “10”. The status of the Extended Fuse bits can
now be read at DATA (“0” means programmed).
5. Set OE to “0”, and BS2, BS1 to “01”. The status of the Lock bits can now be read
at DATA (“0” means programmed).
6. Set OE to “1”.
Figure 144. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
0
Fuse Low Byte
Extended Fuse Byte
Lock Bits
0
1
1
0
DATA
BS2
BS1
Fuse High Byte
1
BS2
Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the
Flash” on page 341 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected Signature byte can now be read at
DATA.
4. Set OE to “1”.
346
ATmega640/1280/1281/2560/2561
2549A–AVR–03/05
ATMEL [ ATMEL ]
