Datasheet

237
7728G–AVR–06/10
ATtiny87/ATtiny167
21.7.12 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 232 for details on Command loading):
1. A: Load Command
“0000 0100
b
”.
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 “1”, and BS1 to “0”. The status of the Extended Fuse bits can
now be read at DATA (“0” means programmed).
5. 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).
6. Set OE
to “1”.
Figure 21-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
21.7.13 Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash”
on page 232 for details on Command and Address loading):
1. A: Load Command
“0000 1000
b
”.
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”.
21.7.14 Reading the 8 MHz RC Oscillator Calibration Byte
The algorithm for reading the 8 MHz RC Oscillator Calibration byte is as follows (refer to “Pro-
gramming the Flash” on page 232 for details on Command and Address loading):
1. A: Load Command
“0000 1000
b
”.
2. B: Load Address Low
Byte, 0x00.
3. Set OE
to “0”, and BS1 to “1”. The 8 MHz RC Oscillator Calibration byte can now be
read at DATA.
4. Set OE
to “1”.
BS2
DATA
0
1
BS2
Extended Fuse Byte
Fuse Low Byte
0
1
Fuse High Byte
Lock Bits
BS1
0
1