Atmel XMEGA B, User Manual

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379 XMEGA B [DATASHEET]
8291B–AVR–01/2013
30.6 Flash and EEPROM Page Buffers
The flash memory is updated page by page. The EEPROM can be updated on a byte-by-byte and page-by-page basis.
flash and EEPROM page programming is done by first filling the associated page buffer, and then writing the entire page
buffer to a selected page in flash or EEPROM.
The size of the page and page buffers depends on the flash and EEPROM size in each device, and details are described
in the device datasheet.
30.6.1 Flash Page Buffer
The flash page buffer is filled one word at a time, and it must be erased before it can be loaded. When loading the page
buffer with new content, the result is a binary AND between the existing content of the page buffer location and the new
value. If the page buffer is already loaded once after erase the location will most likely be corrupted.
Page buffer locations that are not loaded will have the value 0xFFFF, and this value will then be programmed into the
corresponding flash page locations.
The page buffer is automatically erased after:

A device reset

Executing the write flash page command

Executing the erase and write flash page command

Executing the signature row write command

Executing the write lock bit command
30.6.2 EEPROM Page Buffer
The EEPROM page buffer is filled one byte at a time, and it must be erased before it can be loaded. When loading the
page buffer with new content, the result is a binary AND between the existing content of the page buffer location and the
new value. If the EEPROM page buffer is already loaded once after erase the location will most likely be corrupted.
EEPROM page buffer locations that are loaded will get tagged by the NVM controller. During a page write or page erase,
only targed locations will be written or erased. Locations that are not targed will not be written or erased, and the
corresponding EEPROM location will remain unchanged. This means that before an EEPROM page erase, data must be
loaded to the selected page buffer location to tag them. When performing an EEPROM page erase, the actual value of
the tagged location does not matter.
The EEPROM page buffer is automatically erased after:

A system reset

Executing the write EEPROM page command

Executing the erase and write EEPROM page command

Executing the write lock bit and write fuse commands
30.7 Flash and EEPROM Programming Sequences
For page programming, filling the page buffers and writing the page buffer into flash or EEPROM are two separate
operations. The sequence is same for both self-programming and external programming.
30.7.1 Flash Programming Sequence
Before programming a flash page with the data in the flash page buffer, the flash page must be erased. Programming an
un-erased flash page will corrupt its content.
The flash page buffer can be filled either before the erase flash Page operation or between a erase flash page and a
write flash page operation: