Rainbow Electronics ATmega162V - Manual (Page 222)

222
ATmega162/V
2513E–AVR–09/03
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 106 on page 235), 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 95. 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 95. Addressing the Flash during SPM (1)
Notes: 1. The different variables used in Figure 95 are listed in Table 96 on page 229.
2. PCPAGE and PCWORD are listed in Table 106 on page 235.
Bit 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
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