ATmega640/1280/1281/2560/2561
29.5 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, and RAMPZ in the I/O space. The number of bits actually used is
implementation dependent. Note that the RAMPZ register is only implemented when the pro-
gram space is larger than 64K bytes.
Bit
23
15
22
14
21
13
20
12
19
11
18
10
17
16
9
8
RAMPZ
ZH (R31)
ZL (R30)
RAMPZ7
Z15
Z7
RAMPZ6
Z14
Z6
RAMPZ5
Z13
Z5
RAMPZ4
Z12
Z4
RAMPZ3
Z11
Z3
RAMPZ2
Z10
Z2
RAMPZ1
RAMPZ0
Z9
Z1
1
Z8
Z0
0
7
6
5
4
3
2
Since the Flash is organized in pages (see Table 30-7 on page 340), 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 29-3. 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 (E)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 29-3. Addressing the Flash During SPM(Note:)
BIT 15
ZPCMSB
ZPAGEMSB
1
0
Z - REGISTER
0
PCMSB
PAGEMSB
PCWORD
PROGRAM
COUNTER
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Note:
The different variables used in Figure 29-3 are listed in Table 29-9 on page 330.
323
2549L–AVR–08/07
ATMEL [ ATMEL ]
