21

2570L–AVR–08/07

ATmega325/3250/645/6450

8.5

Register Description

8.5.1

EEARH and EEARL – The EEPROM Address Register

• Bits 15..11 – Res: Reserved Bits

These bits are reserved bits in the ATmega325/3250/645/6450 and will always read as zero.

• Bits 10..0 – EEAR10..0: EEPROM Address

The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the

1/2K bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and

1023/2047. The initial value of EEAR is undefined. A proper value must be written before the

EEPROM may be accessed.

Note:

EEAR10 is only valid for ATmega645 and ATmega6450.

8.5.2

EEDR – The EEPROM Data Register

• 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 operation, the

EEDR contains the data read out from the EEPROM at the address given by EEAR.

8.5.3

EECR – The EEPROM Control Register

• Bits 7..4 – Res: Reserved Bits

These bits are reserved bits in the ATmega325/3250/645/6450 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 inter-

rupt 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 set, setting EEWE within four clock cycles will write data to the EEPROM at

Bit

1514

13121110

9

8

0x22 (0x42)

–

–

–

–

–

EEAR10

EEAR9

EEAR8

EEARH

0x21 (0x41)

EEAR7

EEAR6

EEAR5

EEAR4

EEAR3

EEAR2

EEAR1

EEAR0

EEARL

76

54

321

0

Read/Write

R

R

R

R

R

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

X

X

X

X

X

X

XXX

XX

Bit

7

6

543

21

0

0x20 (0x40)

MSB

LSB

EEDR

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

Bit

765432

10

0x1F (0x3F)

––––

EERIE

EEMWE

EEWE

EERE

EECR

Read/Write

R

R

R

R

R/W

R/W

R/W

R/W

Initial Value

000000

X

0