ATtiny45 datasheet(17/196 Pages) ATMEL

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7598H–AVR–07/09

ATtiny25/45/85

• Bit 6 – Res: Reserved Bit

This bit is reserved in the ATtiny25/45/85 and will always read as 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 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 disables the interrupt. The EEPROM Ready Interrupt generates a constant inter-

rupt 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 1 – EEPE: EEPROM Program Enable

The EEPROM Program Enable Signal EEPE is the programming enable signal to the EEPROM.

When EEPE is written, the EEPROM will be programmed according to the EEPMn bits setting.

The EEMPE bit must be written to one before a logical one is written to EEPE, otherwise no

EEPROM write takes place. When the write access time has elapsed, the EEPE bit is cleared

by hardware. When EEPE has been set, the CPU is halted for two cycles before the next

instruction is executed.

• Bit 0 – EERE: EEPROM Read Enable

The EEPROM Read Enable Signal – EERE – is the read strobe to the EEPROM. When the cor-

rect address is set up in the EEAR Register, the EERE bit must be written to one to trigger the

EEPROM read. The EEPROM read access takes one instruction, and the requested data is

available immediately. When the EEPROM is read, the CPU is halted for four cycles before the

next instruction is executed. The user should poll the EEPE bit before starting the read opera-

tion. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change

the EEAR Register.

Table 5-1.

EEPROM Mode Bits

EEPM1

EEPM0

Programming

Time

Operation

3.4 ms

Erase and Write in one operation (Atomic Operation)

1.8 ms

Erase Only

1.8 ms

Write Only

–

Reserved for future use

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