Editing AVR microcontrollers (section)

==== EEPROM ====
Almost all AVR microcontrollers have internal [[EEPROM]] for semi-permanent data storage. Like flash memory, EEPROM can maintain its contents when electrical power is removed.

In most variants of the AVR architecture, this internal EEPROM memory is not mapped into the MCU's addressable memory space. It can only be accessed the same way an external peripheral device is, using special pointer registers and read/write instructions, which makes EEPROM access much slower than other internal RAM.

However, some devices in the SecureAVR (AT90SC) family<ref>[http://www.atmel.com/images/doc1010.pdf Atmel Smart Card ICs]</ref> use a special EEPROM mapping to the data or program memory, depending on the configuration. The XMEGA family also allows the EEPROM to be mapped into the data address space.

Since the number of writes to EEPROM is limited{{snd}} Atmel specifies 100,000 write cycles in their datasheets{{snd}} a well designed EEPROM write routine should compare the contents of an EEPROM address with desired contents and only perform an actual write if the contents need to be changed.