ATtiny167-ESSZ datasheet(218/282 Pages) ATMEL

218 / 282 page

218

7728D–AVR–07/09

ATtiny87/ATtiny167

20.1.3

Performing a Page Write

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

b” 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.

20.2

Addressing the Flash During Self-Programming

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

ters ZL and ZH in the register file. The number of bits actually used is implementation

dependent.

Since the Flash is organized in pages (see Table 21-7 on page 228), 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 Table 20-2 are listed in Table 21-7 on page 228.

Bit

141312

1110

Z15

Z14

Z13

Z12

Z11

Z10

ZH (R31)

ZL (R30)

Bit

PROGRAM MEMORY

Z - POINTER

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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