31.1 Overview

In ATmega48PB, there is no Read-While-Write support and no separate Boot Loader Section. The SPM instruction can be executed from the entire Flash.

The device provides a Self-Programming mechanism for downloading and uploading program code by the MCU itself. The Self-Programming can use any available data interface and associated protocol to read code and write (program) that code into the Program Memory.

The Program Memory is updated in a page by page fashion. Before programming a page with the data stored in the temporary page buffer, the page must be erased. The temporary page buffer is filled with one word at a time using SPM, and the buffer can be filled either before the Page Erase command or between a Page Erase and a Page Write operation:

Alternative 1, fill the buffer before a Page Erase

  • Fill temporary page buffer
  • Perform a Page Erase
  • Perform a Page Write

Alternative 2, fill the buffer after Page Erase

  • Perform a Page Erase
  • Fill temporary page buffer
  • Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page buffer) before the erase, and then be re-written. When using alternative 1, the Boot Loader provides an effective Read-Modify-Write feature which allows the user software to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is already erased. The temporary page buffer can be accessed in a random sequence. It is essential that the page address used in both the Page Erase and Page Write operation is addressing the same page.