ATmega32A datasheet(257/352 Pages) ATMEL

257 / 352 page

257

8155B–AVR–07/09

ATmega32A

Note:

1. “1” means unprogrammed, “0” means programmed

25.7

Addressing the Flash during Self-Programming

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

Since the Flash is organized in pages (see Table 26-5 on page 269), 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 25-3. 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 only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits.

The content of the Z-pointer is ignored and will have no effect on the operation. The LPM

instruction does also use the Z pointer to store the address. Since this instruction addresses the

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

Figure 25-3. Addressing the Flash during SPM(1)

Table 25-4.

Boot Reset Fuse(1)

BOOTRST

Reset Address

Reset Vector = Application reset (address $0000)

Reset Vector = Boot Loader reset (see Table 25-6 on page 263)

Bit

1514131211

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

Z7Z6Z5Z4Z3

Z2Z1Z0

543210

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

ATmega32A Datasheet(PDF) 257 Page - ATMEL Corporation

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