Rainbow Electronics ATtiny861_V - Manual (Page 164)

164
2588B–AVR–11/06
ATtiny261/461/861
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.
21.1 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 22-7 on page 171 ), 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 21-1 . 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 21-1. Addressing the Flash During SPM (1)
Note: 1. The different variables used in Figure 21-1 are listed in Table 22-7 on page 171 .
21.1.1 EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.
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