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8025I–AVR–02/09

ATmega48P/88P/168P/328P

5.6 Register Description

5.6.1 EEARH and EEARL – The EEPROM Address Register

• Bits 15..9 – Res: Reserved Bits

These bits are reserved bits in the ATmega48P/88P/168P/328P and will always read as zero.

• Bits 8..0 – EEAR8..0: EEPROM Address

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

256/512/512/1K bytes EEPROM space. The EEPROM data bytes are addressed linearly

between 0 and 255/511/511/1023. The initial value of EEAR is undefined. A proper value must

be written before the EEPROM may be accessed.

EEAR8 is an unused bit in ATmega48P and must always be written to zero.

5.6.2 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.

5.6.3 EECR – The EEPROM Control Register

• Bits 7..6 – Res: Reserved Bits

These bits are reserved bits in the ATmega48P/88P/168P/328P 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 5-1. While EEPE

Bit 151413121110 9 8

0x22 (0x42) – – – – – – – EEAR8 EEARH

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

76543210

Read/Write RRRRRRRR/W

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 X

XXXXXXXX

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

Atmel ATmega48PV User Manual

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