Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 122)

122

8052B–AVR–09/08

ATmega4HVD/8HVD

23.4 Performing a Page Write

To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and

execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is

ignored. The page address must be written to PCPAGE. Other bits in the Z-pointer must be

written to zero during this operation.

• The CPU is halted during the Page Write operation.

23.5 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 24-6 on page 131), 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 23-1. Note that the Page Erase and Page Write operations are

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

same page in both the Page Erase and Page Write operation.

The LPM instruction uses 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 23-1. Addressing the Flash During SPM

(1)

Note: 1. The different variables used in Figure 23-1 are listed in Table 24-6 on page 131.

Bit 151413121110 9 8

ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8

ZL (R30) Z7Z6Z5Z4Z3Z2Z1Z0

76543210

PROGRAM MEMORY

0115

Z - REGISTER

BIT

ZPAGEMSB

WORD ADDRESS

WITHIN A PAGE

PAGE ADDRESS

WITHIN THE FLASH

ZPCMSB

INSTRUCTION WORD

PAG E

PCWORD[PAGEMSB:0]:

PAGEEND

PAG E

PCWORDPCPAGE

PCMSB

PAGEMSB

PROGRAM

COUNTER

1 2 ... 117 118 119 120 121 122 123 124 125 126 127 ... 167 168

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