
21
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
5.5.3
EEDR – 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.
5.5.4
EECR – EEPROM Control Register
Bit 7 – Res: Reserved Bit
This bit is reserved for future use and will always read as 0 in ATtiny25/45/85. For compatibility with future AVR
devices, always write this bit to zero. After reading, mask out this bit.
Bit 6 – Res: Reserved Bit
This bit is reserved in the ATtiny25/45/85 and will always read as zero.
Bits 5:4 – EEPM[1:0]: EEPROM Programming Mode Bits
The EEPROM Programming mode bits setting defines which programming action that will be triggered when writ-
ing 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 dis-
ables the interrupt. The EEPROM Ready Interrupt generates a constant interrupt when Non-volatile memory is
ready for programming.
Bit 2 – EEMPE: EEPROM Master Program Enable
The EEMPE bit determines whether writing EEPE to one will have effect or not.
When EEMPE is set, setting EEPE within four clock cycles will program the EEPROM at the selected address. If
EEMPE is zero, setting EEPE will have no effect. When EEMPE has been written to one by software, hardware
clears the bit to zero after four clock cycles.
Bit
7
654321
0
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
EEDR
Read/Write
R/W
Initial Value
0
000000
0
Bit
7
654321
0
–
EEPM1
EEPM0
EERIE
EEMPE
EEPE
EERE
EECR
Read/Write
R
R/W
Initial Value
0
X
0
X
0
Table 5-1.
EEPROM Mode Bits
EEPM1
EEPM0
Programming
Time
Operation
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
–
Reserved for future use