Datasheet

7728G–AVR–06/10

ATtiny87/ATtiny167

• Bit 7:1 – Reserved Bits

These bits are reserved for future use and will always read as 0 in ATtiny87/167.

• Bits 8:0 – EEAR8:0: EEPROM Address

The EEPROM Address Registers – EEARH and EEARL – specifies the high EEPROM

address in the EEPROM space (see “E2 size” in Table 3-1 on page 15). The EEPROM data

bytes are addressed linearly between 0 and “E2 size”. The initial value of EEAR is undefined.

A proper value must be written before the EEPROM may be accessed.

Note: For information only - ATtiny47: EEAR8 exists as register bit but it is not used for addressing.

3.5.2 EEDR – 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.

3.5.3 EECR – EEPROM Control Register

• Bit 7,6 – Res: Reserved Bits

These bits are reserved for future use and will always read as 0 in ATtiny87/167. After reading,

mask out these bits. For compatibility with future AVR devices, always write these bits to zero.

• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits

The EEPROM Programming mode bits 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 differ-

ent operations. The Programming times for the different modes are shown in Table 3-2. 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 76543210

EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 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 3-2. EEPROM Mode Bits

EEPM1 EEPM0

Typical

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