ATmega48/88/168
•
The CPU is halted during the Page Write operation.
Addressing the Flash
During Self-
Programming
The Z-pointer is used to address the SPM commands.
Bit
15
Z15
Z7
7
14
Z14
Z6
6
13
Z13
Z5
5
12
Z12
Z4
4
11
Z11
Z3
3
10
Z10
Z2
2
9
Z9
Z1
1
8
Z8
Z0
0
ZH (R31)
ZL (R30)
Since the Flash is organized in pages (see Table 122 on page 274), 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 118. Note that the Page Erase
and Page Write operations are addressed independently. Therefore it is of major impor-
tance 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 115. Addressing the Flash During SPM(1)
BIT 15
ZPCMSB
ZPAGEMSB
1
0
0
Z - REGISTER
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:
1. The different variables used in Figure 118 are listed in Table 122 on page 274.
249
2545D–AVR–07/04
ATMEL [ ATMEL ]
