Rainbow Electronics ATmega8HVD - Manual (Page 122)

122
8052B–AVR–09/08
ATmega4HVD/8HVD
23.4 Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is
ignored. The page address must be written to PCPAGE. Other bits in the Z-pointer must be
written to zero during this operation.
• The CPU is halted during the Page Write operation.
23.5 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 24-6 on page 131 ), 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 23-1 . Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance 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 23-1. Addressing the Flash During SPM (1)
Note: 1. The different variables used in Figure 23-1 are listed in Table 24-6 on page 131 .
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