AT90SCR100 datasheet(369/433 Pages) ATMEL

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369

TPR0327AY–SMS–30Jan09

AT90SCR100

28.6

Addressing the Flash During Self-Programming

The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers

ZL and ZH in the register file. The number of bits actually used is implementation dependent.

Since the Flash is organized in pages (see Table 29-7 on page 381), the Program Counter can

be treated as having two different sections. One section, consisting of the least significant bits, is

addressing the words within a page, while the most significant bits are addressing the pages.

This is shown in Figure 28-3. Note that the Page Erase and Page Write operations are

addressed independently. Therefore it is of major importance that the Boot Loader software

addresses the same page in both the Page Erase and Page Write operation. Once a program-

ming operation is initiated, the address is latched and the Z-pointer can be used for other

operations.

The (E)LPM instruction use the Z-pointer to store the address. Since this instruction addresses

the Flash byte-by-byte, also bit Z0 of the Z-pointer is used.

Figure 28-3.

Addressing the Flash During SPM

Bit

151413

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZH (R30)

76543

Only one SPM instruction should be active at any time.

PROGRAM MEMORY

Z - REGISTER

BIT

ZPAGEMSB

WORD ADDRESS

WITHIN A PAGE

PAGE ADDRESS

WITHIN THE FLASH

ZPCMSB

INSTRUCTION WORD

PAGE

PCWORD[PAGEMSB:0]:

PAGEEND

PAGE

PCWORD

PCPAGE

PCMSB

PAGEMSB

PROGRAM

COUNTER

Note

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