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20
8154B–AVR–07/09
ATmega16A
Bits 15:9 – Res: Reserved Bits
These bits are reserved bits in the ATmega16A 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.
7.6.2
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.
7.6.3
EECR – The EEPROM Control Register
Bits 7:4 – Res: Reserved Bits
These bits are reserved bits in the ATmega16A and will always read as zero.
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 inter-
rupt when EEWE is cleared.
Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written.
When EEMWE is set, setting EEWE within four clock cycles will write data to the EEPROM at
the selected address If EEMWE is zero, setting EEWE will have no effect. When EEMWE has
been written to one by software, hardware clears the bit to zero after four clock cycles. See the
description of the EEWE bit for an EEPROM write procedure.
Bit 1 – EEWE: EEPROM Write Enable
The EEPROM Write Enable Signal EEWE is the write strobe to the EEPROM. When address
and data are correctly set up, the EEWE bit must be written to one to write the value into the
EEPROM. The EEMWE bit must be written to one before a logical one is written to EEWE, oth-
erwise no EEPROM write takes place. The following procedure should be followed when writing
the EEPROM (the order of steps 3 and 4 is not essential):
Bit
765
432
10
MSB
LSB
EEDR
Read/Write
R/W
Initial Value
0
Bit
7
6543
2
1
0
–
EERIE
EEMWE
EEWE
EERE
EECR
Read/Write
RRRR
R/W
Initial Value0
0000
0
X
0