ATEMGA128 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'ATEMGA128' PDF : 395 Pages View PDF
EEPROM Data Register –
EEDR
EEPROM Control Register –
EECR
These are reserved bits and will always read as zero. When writing to this address loca-
tion, write these bits to zero for compatibility with future devices.
• Bits 11..0 – EEAR11..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL – specify the EEPROM
address in the 4K bytes EEPROM space. The EEPROM data bytes are addressed lin-
early between 0 and 4096. The initial value of EEAR is undefined. A proper value must
be written before the EEPROM may be accessed.
Bit
Read/Write
Initial Value
7
6
MSB
R/W
R/W
0
0
5
R/W
0
4
R/W
0
3
R/W
0
2
R/W
0
1
R/W
0
0
LSB
R/W
0
EEDR
• Bits 7..0 – EEDR7.0: EEPROM Data
For the EEPROM write operation, the EEDR Register contains the data to be written to
the EEPROM in the address given by the EEAR Register. For the EEPROM read oper-
ation, the EEDR contains the data read out from the EEPROM at the address given by
EEAR.
Bit
7
6
5
4
3
2
1
0
–
–
–
–
EERIE EEMWE EEWE EERE
EECR
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
X
0
• Bits 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATmega128 and will always read as zero.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set.
Writing EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a
constant interrupt when EEWE is cleared.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be
written. When EEMWE is written to one, writing EEWE to one within four clock cycles
will write data to the EEPROM at the selected address. If EEMWE is zero, writing EEWE
to one will have no effect. When EEMWE has been written to one by software, hardware
clears the bit to zero after four clock cycles. See the description of the EEWE bit for an
EEPROM write procedure.
• Bit 1 – EEWE: EEPROM Write Enable
The EEPROM Write Enable Signal EEWE is the write strobe to the EEPROM. When
address and data are correctly set up, the EEWE bit must be set to write the value into
the EEPROM. The EEMWE bit must be set when the logical one is written to EEWE,
otherwise no EEPROM write takes place. The following procedure should be followed
when writing the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEWE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
22 ATmega128
2467O–AVR–10/06
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