at90pwm81-16se ATMEL Corporation, at90pwm81-16se Datasheet - Page 240

• Manufacturer Part Number: at90pwm81-16se
• Description: 8-bit Avr Microcontroller With 8k Bytes In- System Programmable Flash
• Manufacturer: ATMEL Corporation

21.7
240
Self-Programming the Flash
AT90PWM81
Figure 21-3.
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 buffer 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 tem-
porary 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 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. See
page 244
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
Z - REGISTER
1. The different variables used in
for an assembly code example.
PROGRAM MEMORY
BIT
Addressing the Flash During SPM
PAGE
PROGRAM
COUNTER
15
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
PCMSB
PCPAGE
Figure 21-3
ZPAGEMSB
PAGEMSB
PCWORD
“Simple Assembly Code Example for a Boot Loader” on
(1)
are listed in
WORD ADDRESS
WITHIN A PAGE
1
0
0
INSTRUCTION WORD
Table 21-9 on page
PAGE
247.
PCWORD[PAGEMSB:0]:
00
01
02
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