Rainbow-electronics ATmega8515L Manuale Utente Scaricare il pdf (Pagina 168)

168

ATmega8515(L)

2512A–AVR–04/02

Figure 73. Addressing the Flash during SPM

(1)

Note: 1. The different variables used in Figure 73 are listed in Table80onpage 174.

Self-Programming the

Flash

The program memory is updated in a page by page fashion. Before programming a

page with the data stored in thetemporary page buffer, the page must beerased.The

temporary page buffer isfilled one word atatimeusing SPM and the buffercan be filled

eitherbeforethe page erase command orbetween a Page Eraseand a Page Write

operation:

Alternative 1,fill the bufferbeforeaPageErase:

• 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 partof the page needs to be changed, the restof the page must be stored(for

exampleinthetemporary page buffer) beforetheerase, and then be rewritten. When

using alternative 1, the Boot Loaderprovides an effective Read-Modify-Write feature

which allows theusersoftwaretofirst read the page,dothenecessary changes, and

then write back themodifieddata. If alternative 2 is used, it is not possibletoread the

old data while loading sincethe page is already erased.Thetemporary page buffercan

beaccessed in a random sequence. Itis essential that the page address used in both

the Page Eraseand Page Write operation is addressing the same page. See “Simple

Assembly Code Example for a Boot Loader”onpage 171 for an assembly code

example.

PROGRAM MEMORY

0115

Z - REGISTER

BIT

ZPAGEMSB

WORD ADDRESS

WITHIN A PAGE

PAGE ADDRESS

WITHIN THE FLASH

ZPCMSB

INSTRUCTION WORD

PAGE

PCWORD[PAGEMSB:0]:

PAGEEND

PAGE

PCWORDPCPAGE

PCMSB

PAGEMSB

PROGRAM

COUNTER

1 2 ... 163 164 165 166 167 168 169 170 171 172 173 ... 222 223

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