Rainbow-electronics ATtiny861_V Uživatelský manuál stáhnout pdf (Strana 164)

164

2588B–AVR–11/06

ATtiny261/461/861

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.

21.1 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 22-7 on page 171), 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 21-1. 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 21-1. Addressing the Flash During SPM

(1)

Note: 1. The different variables used in Figure 21-1 are listed in Table 22-7 on page 171.

21.1.1 EEPROM Write Prevents Writing to SPMCSR

Note that an EEPROM write operation will block all software programming to Flash. Reading the

Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It

is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies

that the bit is cleared before writing to the SPMCSR Register.

Bit 1514131211109 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 ... 159 160 161 162 163 164 165 166 167 168 169 ... 235 236

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