Atmel ATmega8535L User Manual page 247

Programming the Lock Bits
Reading the Fuse and Lock
Bits
Reading the Signature Bytes
Reading the Calibration Byte
2502K–AVR–10/06
The algorithm for programming the Lock bits is as follows (refer to "Programming the
Flash" on page 243 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.
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.
The algorithm for reading the Fuse and Lock bits is as follows (refer to "Programming
the Flash" on page 243 for details on Command loading):
1. A: Load Command "0000 0100".
2. Set OE to "0", BS2 to "0", and BS1 to "0". The status of the Fuse Low bits can
now be read at DATA ("0" means programmed).
3. Set OE to "0", BS2 to "1", and BS1 to "1". The status of the Fuse High bits can
now be read at DATA ("0" means programmed).
4. Set OE to "0", BS2 to "0", and BS1 to "1". The status of the Lock bits can now be
read at DATA ("0" means programmed).
5. Set OE to "1".
Figure 120. Mapping Between BS1, BS2 and the Fuse- and Lock Bits During Read
Fuse Low Byte
Lock Bits
Fuse High Byte
The algorithm for reading the Signature bytes is as follows (refer to "Programming the
Flash" on page 243 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".
The algorithm for reading the Calibration byte is as follows (refer to "Programming the
Flash" on page 243 for details on Command and Address loading):
1. A: Load Command "0000 1000".
2. B: Load Address Low Byte, 0x00.
3. Set OE to "0", and BS1 to "1". The Calibration byte can now be read at DATA.
4. Set OE to "1".
0
BS1
1
BS2
ATmega8535(L)
0
DATA
1
247