Datasheet

217
ATmega8A [DATASHEET]
8159E–AVR–02/2013
4. Give WR a negative pulse and wait for RDY/BSY to go high.
25.7.9 Programming the Fuse High Bits
The algorithm for programming the Fuse high bits is as follows (refer to “Programming the Flash” on page 213 for
details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR
a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
25.7.10 Programming the Lock Bits
The algorithm for programming the Lock Bits is as follows (refer to “Programming the Flash” on page 213 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.
25.7.11 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 213 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 25-3. Mapping Between BS1, BS2 and the Fuse- and Lock Bits During Read
Fuse low byte
Lock bits
0
1
BS2
Fuse high byte
0
1
BS1
DATA