ATtiny45 datasheet(131/196 Pages) ATMEL

131 / 196 page

131

7598H–AVR–07/09

ATtiny25/45/85

20.3

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.

20.4

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 21-6 on page 137), 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 20-1. 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 20-1. Addressing the Flash During SPM

(1)

Note:

1. The different variables used in Figure 20-1 are listed in Table 21-6 on page 137.

Bit

1514131211

ZH (R31)

Z15

Z14

Z13

Z12

Z11

Z10

ZL (R30)

Z7Z6Z5Z4Z3

Z1Z0

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

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