ATmega8A Boot Loader Parameters

In the following tables, the parameters used in the description of the self programming are given.

Table 1. Boot Size Configuration, ATmega8A
BOOTSZ1	BOOTSZ0	Boot Size	Pages	Application Flash Section	Boot Loader Flash Section	End Application Section	Boot Reset Address (Start Boot Loader Section)
1	1	128 words	4	0x000 - 0xF7F	0xF80 - 0xFFF	0xF7F	0xF80
1	0	256 words	8	0x000 - 0xEFF	0xF00 - 0xFFF	0xEFF	0xF00
0	1	512 words	16	0x000 - 0xDFF	0xE00 - 0xFFF	0xDFF	0xE00
0	0	1024 words	32	0x000 - 0xBFF	0xC00 - 0xFFF	0xBFF	0xC00

Note: The different BOOTSZ Fuse configurations are shown in Figure 2.

Table 2. Read-While-Write Limit, ATmega8A
Section	Pages	Address
Read-While-Write section (RWW)	96	0x000 - 0xBFF
No Read-While-Write section (NRWW)	32	0xC00 - 0xFFF

Table 3. Explanation of Different Variables used in Figure and the Mapping to the Z-pointer, ATmega8A
Variable		Corresponding Z-value⁽¹⁾	Description
PCMSB	11		Most significant bit in the Program Counter. (The Program Counter is 12 bits PC[11:0])
PAGEMSB	4		Most significant bit which is used to address the words within one page (32 words in a page requires 5 bits PC [4:0]).
ZPCMSB		Z12	Bit in Z-register that is mapped to PCMSB. Because Z0 is not used, the ZPCMSB equals PCMSB + 1.
ZPAGEMSB		Z5	Bit in Z-register that is mapped to PAGEMSB. Because Z0 is not used, the ZPAGEMSB equals PAGEMSB + 1.
PCPAGE	PC[11:5]	Z12:Z6	Program counter page address: Page select, for page erase and page write
PCWORD	PC[4:0]	Z5:Z1	Program counter word address: Word select, for filling temporary buffer (must be zero during page write operation)

Note: 1.

Z15:Z13: always ignored.

Z0: should be zero for all SPM commands, byte select for the LPM instruction.

See Addressing the Flash During Self-Programming for details about the use of Z-pointer during Self- Programming.

8-bit AVR Microcontroller