Datasheet

159
7701F–AVR–10/12
Atmel ATtiny24/44/84 [Preliminary]
20.3 Performing a Page Write
To execute a 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 are
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.
20.4 Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands.
Because the Flash is organized in pages (see Table 21-7 on page 166), 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 on page 167. 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. Because this instruction
addresses the flash byte-by-byte, the LSB (bit Z0) of the Z-pointer is also used.
Figure 20-1. Addressing the Flash During SPM
(1)
Note: 1. The different variables used in Figure 20-1 are listed in Table 21-7 on page 166.
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