Data Sheet

257
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
26.1.3 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.
26.2 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 28-11 on page 286), 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 27-3 on page 269. 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 26-1. Addressing the Flash During SPM
(1)
Note: 1. The different variables used in Figure 27-3 are listed in Table 28-11 on page 286.
26.2.1 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 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0
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