Programming the EEPROM
The programming algorithm for the EEPROM data memory is as follows (refer to “Pro-
gramming the Flash” for details on command, address and data loading):
1. A: Load Command “0001 0001”.
2. C: Load Address Low Byte ($00 - $3F).
3. D: Load Data Low Byte ($00 - $FF).
4. E: Write Data Low Byte.
Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the
Flash” for details on command and address loading):
1. A: Load Command “0000 0011”.
2. C: Load Address Low Byte ($00 - $3F).
3. Set OE to “0”, and BS to “0”. The EEPROM data byte can now be read at DATA.
4. Set OE to “1”.
Programming the Fuse Bits
The algorithm for programming the Fuse bits is as follows (refer to “Programming the
Flash” for details on command and data loading):
1. A: Load Command “0100 0000”.
2. D: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
Bit 5 = SPIEN Fuse
Bit 0 = RCEN Fuse
Bit 7 - 6, 4 - 1 = “1”. These bits are reserved and should be left unprogrammed (“1”).
3. Give WR a tWLWH_PFB wide negative pulse to execute the programming; tWLWH_PFB
is found in Table 17. Programming the Fuse bits does not generate any activity
on the RDY/BSY pin.
Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the
Flash” for details on command and data loading):
1. A: Load Command “0010 0000”.
2. D: Load Data Low Byte. Bit n = “0” programs the Lock bit.
Bit 2 = Lock Bit2
Bit 1 = Lock Bit1
Bit 7 - 3, 0 = “1”. These bits are reserved and should be left unprogrammed (“1”).
3. E: Write Data Low Byte.
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 39 for details on command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, and BS to “1”. The status of Fuse and Lock bits can now be read
at DATA (“0” means programmed).
Bit 7 = Lock Bit1
Bit 6 = Lock Bit2
Bit 5 = SPIEN Fuse
Bit 0 = RCEN Fuse
3. Set OE to “1”.
Observe especially that BS needs to be set to “1”.
42
AT90S1200
0838H–AVR–03/02
ATMEL [ ATMEL ]
