Datasheet

2549O–AVR–05/12

ATmega640/1280/1281/2560/2561

9.2 Register Description

9.2.1 EEPROM registers

9.2.1.1 EEARH and EEARL – The EEPROM Address Register

• Bits 15:12 – Res: Reserved Bits

These bits are reserved bits and will always read as zero.

• Bits 11:0 – EEAR8:0: EEPROM Address

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

4Kbytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and

4096. The initial value of EEAR is undefined. A proper value must be written before the

EEPROM may be accessed.

9.2.1.2 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.

9.2.1.3 EECR – The EEPROM Control Register

• Bits 7:6 – Res: Reserved Bits

These bits are reserved bits and will always read as zero.

• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits

The EEPROM Programming mode bit setting defines which programming action that will be trig-

gered when writing EEPE. It is possible to program data in one atomic operation (erase the old

value and program the new value) or to split the Erase and Write operations in two different

operations. The Programming times for the different modes are shown in Table 9-1 on page 36.

While EEPE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be

reset to 0b00 unless the EEPROM is busy programming.

Bit 15141312 11 10 9 8

0x22 (0x42) ––––EEAR11EEAR10EEAR9EEAR8EEARH

0x21 (0x41) EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL

7654 3 2 10

Read/Write RRRRR/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value0000X XXX

XXXX X X XX

Bit 76543210

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 76543210

0x1F (0x3F) – – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR

Read/Write R R R/W R/W R/W R/W R/W R/W

Initial Value 0 0 X X 0 0 X 0