Datasheet
240
7799D–AVR–11/10
ATmega8U2/16U2/32U2
23.8.15 ATmega16U2 Boot Loader Parameters
In Table 23-11 through Table 23-13, the parameters used in the description of the Self-Programming are given.
(Page size = 64 words = 128 bytes)
Note: 1. The different BOOTSZ Fuse configurations are shown in Figure 23-2.
Note: 1. For details about these two section, see “NRWW – No Read-While-Write Section” on page 227 and “RWW – Read-While-
Write Section” on page 227.
Note: 1. Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.
See “Addressing the Flash During Self-Programming” on page 232 for details about the use of Z-pointer during Self-
Programming.
Table 23-11. Boot Size Configuration
(1)
(Word Addresses)
BOOTSZ1
BOOTSZ0
Boot Size
Pages
Application
Flash Section
Boot Loader
Flash Section
End
Application
Section
Boot
Reset Address
(Start Boot
Loader Section)
1 1 256 words 4 0x0000 - 0x1EFF 0x1F00 - 0x1FFF 0x1EFF 0x1F00
1 0 512 words 8 0x0000 - 0x1DFF 0x1E00 - 0x1FFF 0x1DFF 0x1E00
0 1 1024 words 16 0x0000 - 0x1BFF 0x1C00 - 0x1FFF 0x1BFF 0x1C00
0 0 2048 words 32 0x0000 - 0x17FF 0x1800 - 0x1FFF 0x17FF 0x1800
Table 23-12. Read-While-Write Limit
(1)
Section Pages Address
Read-While-Write section (RWW) 96 0x0000 - 0x17FF
No Read-While-Write section (NRWW) 32 0x1800 - 0x1FFF
Table 23-13. Explanation of different variables used in Figure 23-4 and the mapping to the Z-pointer
Variable
Corresponding
Z-value Description
(1)
PCMSB 12
Most significant bit in the Program Counter. (The Program
Counter is 13 bits PC[12:0])
PAGEMSB 5
Most significant bit which is used to address the words within
one page (64 words in a page requires six bits PC [5:0]).
ZPCMSB Z13
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not
used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB Z6
Bit in Z-pointer that is mapped to PCMSB. Because Z0 is not
used, the ZPAGEMSB equals PAGEMSB + 1.
PCPAGE PC[12:6] Z13:Z7
Program Counter page address: Page select, for Page Erase
and Page Write
PCWORD PC[5:0] Z6:Z1
Program Counter word address: Word select, for filling
temporary buffer (must be zero during Page Write operation)