Datasheet

18
ATmega8A [DATASHEET]
8159E–AVR–02/2013
be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to
these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory
addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will
operate on all bits in the I/O Register, writing a one back into any flag read as set, thus clearing the flag. The CBI
and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
8.6 Register Description
8.6.1 EEARH and EEARL – The EEPROM Address Register
• Bits 15:9 – Res: Reserved Bits
These bits are reserved bits in the ATmega8A 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 512 bytes
EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 511. The initial value of EEAR is
undefined. A proper value must be written before the EEPROM may be accessed.
8.6.2 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.
8.6.3 EECR – The EEPROM Control Register
• Bits 7:4 – Res: Reserved Bits
These bits are reserved bits in the ATmega8A and will always read as zero.
Bit 151413121110 9 8
–––––––EEAR8EEARH
EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
76543210
Read/WriteRRRRRRRR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
XXXXXXXX
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
– – – – EERIE EEMWE EEWE EERE EECR
Read/Write R R R R R/W R/W R/W R/W
Initial Value000000X0