Datasheet

ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
20
8.6 Register Description
8.6.1 EEARH and EEARL – The EEPROM Address Register
• Bits 15:9] – Reserved
These bits are reserved bits in the Atmel
®
ATmega48PA/88PA/168PA and will always read as zero.
• Bits 8:0 – EEAR[8:0]: 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 the Atmel ATmega48PA and must always be written to zero.
8.6.2 EEDR – The EEPROM Data Register
• Bits 7:0 – EEDR[7:0]: 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.
8.6.3 EECR – The EEPROM Control Register
• Bits 7:6 – Reserved
These bits are reserved bits in the Atmel ATmega48PA/88PA/168PA 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 8-1.
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 151413121110 9 8
0x22 (0x42) –––––––EEAR8EEARH
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 Value0000000X
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 Value00000000
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