8-bit AVR Microcontrollers

EEPROM Read/Write Access

The EEPROM access registers are accessible in the I/O space.

The write access time for the EEPROM is given in Table 2. A self-timing function, however, lets the user software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some precautions must be taken. In heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This causes the device for some period of time to run at a voltage lower than specified as a minimum for the clock frequency used. Refer to Preventing EEPROM Corruption for details on how to avoid problems in these situations.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to the description of the EEPROM Control register for details on this.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.