AT45DB021A

25

Figure 2. Algorithm for Randomly Modifying Data

Notes:

1. To preserve data integrity, each page of a DataFlash sector must be updated/rewritten at least once within every 10,000

cumulative page erase/program operations.

2. A Page Address Pointer must be maintained to indicate which page is to be rewritten. The Auto Page Rewrite command

must use the address specified by the Page Address Pointer.

3. Other algorithms can be used to rewrite portions of the Flash array. Low power applications may choose to wait until 10,000

cumulative page erase/program operations have accumulated before rewriting all pages of the sector. See application note

AN-4 (“Using Atmel’s Serial DataFlash”) for more details.

Sector Addressing

PA9

PA8

PA7

PA6

PA5

PA4

PA3

PA2-PA0

Sector

000

0000

X

0

0

0

XX

XXX

X

1

0

1

XX

XXX

X

2

1

XXX

XXX

X

3

START

MAIN MEMORY PAGE

TO BUFFER TRANSFER

(53H, 55H)

INCREMENT PAGE

ADDRESS POINTER

(2)

AUTO PAGE REWRITE

(2)

(58H, 59H)

END

provide address of

page to modify

If planning to modify multiple

bytes currently stored within

a page of the Flash array

MAIN MEMORY PAGE PROGRAM

THROUGH BUFFER

(82H, 85H)

BUFFER WRITE

(84H, 87H)

BUFFER TO MAIN

MEMORY PAGE PROGRAM

(83H, 86H)