ATMEGA128-16AU SL383 Atmel, ATMEGA128-16AU SL383 Datasheet - Page 279

• Manufacturer Part Number: ATMEGA128-16AU SL383
• Manufacturer: Atmel

Self-Programming
the Flash
2467S–AVR–07/09
Figure 134. Addressing the Flash During SPM
Notes:
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
•
•
•
Alternative 2, fill the buffer after page erase
•
•
•
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
code example.
Fill temporary page buffer
Perform a page erase
Perform a page write
Perform a page erase
Fill temporary page buffer
Perform a page write
1. The different variables used in
2. PCPAGE and PCWORD are listed in
RAMPZ
PROGRAM
COUNTER
PROGRAM MEMORY
“Simple Assembly Code Example for a Boot Loader” on page 282
PAGE
PCMSB
PAGE ADDRESS
WITHIN THE FLASH
BIT
15
ZPCMSB
PCPAGE
Figure 134
Table 124 on page
PAGEMSB
ZPAGEMSB
(1)
WORD ADDRESS
WITHIN A PAGE
PCWORD
are listed in
INSTRUCTION WORD
1
Table 114 on page
PAGE
0
0
292.
Z - REGISTER
ATmega128
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
285.
for an assembly
279