ATMEGA640 datasheet(314/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

29.5 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

the RAMPZ register is only implemented when the program space is larger than 64Kbytes.

Since the Flash is organized in pages (see Table 30-7 on page 328), the Program Counter can be treated as hav-

ing 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 29-3. 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 29-3. Addressing the Flash During SPM(1)

Note:

1. The different variables used in Figure 29-3 are listed in Table 29-9 on page 320.

Bit

23222120

19181716

RAMPZ

RAMPZ7

RAMPZ6

RAMPZ5

RAMPZ4

RAMPZ3

RAMPZ2

RAMPZ1

RAMPZ0

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

6543

210

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

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