Datasheet

329
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
Note: 1. For details about these two section, see NRWWNo Read-While-Write Section” on page
318 and “RWW Read-While-Write Section” on page 318.
Note: 1. Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.
2. See “Addressing the Flash During Self-Programming” on page 322 for details about the use of
Z-pointer during Self-Programming.
Table 29-8. Read-While-Write Limit, ATmega640
Section
(1)
Pages Address
Read-While-Write section (RWW) 224 0x0000 - 0x6FFF
No Read-While-Write section (NRWW) 32 0x7000 - 0x7FFF
Table 29-9. Explanation of different variables used in Figure 29-3 on page 322 and the map-
ping to the Z-pointer, ATmega640
Variable
Corresponding
Z-value
(2)
Description
(1)
PCMSB 14
Most significant bit in the Program Counter.
(The Program Counter is 15 bits PC[14:0]).
PAG EM SB 6
Most significant bit which is used to address
the words within one page (128 words in a
page requires seven bits PC [6:0]).
ZPCMSB Z15
Bit in Z-pointer that is mapped to PCMSB.
Because Z0 is not used, the ZPCMSB equals
PCMSB + 1.
ZPAGEMSB Z7
Bit in Z-pointer that is mapped to PCMSB.
Because Z0 is not used, the ZPAGEMSB
equals PAGEMSB + 1.
PCPAGE PC[14:7] Z15:Z8
Program Counter page address: Page select,
for Page Erase and Page Write.
PCWORD PC[6:0] Z7:Z1
Program Counter word address: Word select,
for filling temporary buffer (must be zero
during Page Write operation).