ATMEGA164P_1 Datasheet, PDF (284/377 Pages) ATMEL Corporation – 8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash

24.7 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers
ZL and ZH in the register file.
Bit
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
ZH (R31)
Z15
Z14
Z13
Z12
Z11
Z10
Z9
Z8
ZL (R30)
Z7
Z6
Z5
Z4
Z3
Z2
Z1
Z0
7
6
5
4
3
2
1
0
Since the Flash is organized in pages (see Table 25-7 on page 299), 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 24-3. 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 program-
ming operation is initiated, the address is latched and the Z-pointer can be used for other
operations.
The LPM instruction use the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also bit Z0 of the Z-pointer is used.
Figure 24-3. Addressing the Flash During SPM⁽¹⁾
BIT 15
Z - REGISTER
ZPCMSB
ZPAGEMSB 1 0
0
PCMSB
PROGRAM
COUNTER
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PAGEMSB
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note: 1. The different variables used in Figure 24-3 are listed in Table 24-9 on page 291.
284 ATmega164P/324P/644P
7674F–AVR–09/09