
266
ATmega64A [DATASHEET]
8160D–AVR–02/2013
27.7
Addressing the Flash During Self-programming
The Z-pointer is used to address the SPM commands.
ing 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 27-3. 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 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.
Notes:
27.8
Self-programming the Flash
The program memory is updated in a page-by-page fashion. Before programming a page with the data stored in
the temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using
SPM and the buffer can be filled either before the Page Erase command or between a Page Erase and a Page
Write operation:
Alternative 1, fill the buffer before a Page Erase:
Fill temporary page buffer
Bit
151413121110
9
8
ZH (R31)
Z15
Z14
Z13
Z12
Z11
Z10
Z9
Z8
ZL (R30)
Z7Z6Z5Z4Z3Z2Z1Z0
7
6543210
PROGRAM MEMORY
0
1
15
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
PCWORD
PCPAGE
PCMSB
PAGEMSB
PROGRAM
COUNTER