Datasheet

ATmega48/88/168 Automotive [DATASHEET]

7530K–AVR–07/14

• Bits 15..9 – Res: Reserved Bits

These bits are reserved bits in the Atmel

ATmega48/88/168 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 bytes EEPROM

space. The EEPROM data bytes are addressed linearly between 0 and 255/511/511. 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 ATmega48 and must always be written to zero.

5.3.3 The EEPROM Data Register – 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 operation, the EEDR contains the data read out from the EEPROM at the address

given by EEAR.

5.3.4 The EEPROM Control Register – EECR

• Bits 7..6 – Res: Reserved Bits

These bits are reserved bits in the Atmel ATmega48/88/168 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 triggered 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 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 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 EEPE is cleared.

Bit 76543210

MSB LSB EEDR

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

Initial Value00000000

Bit 76543210

– – 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

Table 5-1. EEPROM Mode Bits

EEPM1 EEPM0 Programming Time Operation

0 0 3.4 ms Erase and write in one operation (atomic operation)

0 1 1.8 ms Erase only

1 0 1.8 ms Write only

1 1 – Reserved for future use