ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 275

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

27.8
2545T–AVR–05/11
Self-programming the flash
Figure 27-3. Addressing the flash during SPM
Note:
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 buf-
fer is filled 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 rewritten. 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 alter-
native 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. See
example.
Z - REGISTER
1. The different variables used in
PROGRAM MEMORY
“Simple assembly code example for a boot loader” on page 279
BIT
PAGE
PROGRAM
COUNTER
15
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
PCMSB
PCPAGE
Figure 27-3
ZPAGEMSB
PAGEMSB
PCWORD
(1)
WORD ADDRESS
WITHIN A PAGE
.
are listed in
1
0
0
INSTRUCTION WORD
PAGE
Table 27-8 on page
ATmega48/88/168
for an assembly code
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
281.
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