Datasheet

283
2490R–AVR–02/2013
ATmega64(L)
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 123 on page 296), 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 137. 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 programming operation is
initiated, the address is latched and the Z-pointer can be used for other operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits.
The content of the Z-pointer is ignored and will have no effect on the operation. The LPM
instruction does also use 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 137. Addressing the Flash during SPM
(1)
Table 2 on page 283
Notes: 1. The different variables used in Figure 137 are listed in Table 113 on page 289.
2. PCPAGE and PCWORD are listed in Table 124 on page 296.
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7Z6Z5Z4Z3Z2Z1Z0
76543210
PROGRAM MEMORY
0115
Z - REGISTER
BIT
0
ZPAGEMSB
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
INSTRUCTION WORD
PAGE
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PAGE
PCWORDPCPAGE
PCMSB
PAGEMSB
PROGRAM
COUNTER