ATmega162 datasheet(223/324 Pages) ATMEL

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223

2513K–AVR–07/09

ATmega162/V

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 105 on page 236), 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 95. 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 programming 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 95. Addressing the Flash during SPM(1)

Notes:

1. The different variables used in Figure 95 are listed in Table 95 on page 230.

2. PCPAGE and PCWORD are listed in Table 105 on page 236.

Bit

151413

1211

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

Z7Z6

Z5Z4Z3

Z2Z1Z0

765

432

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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