ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 283

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Addressing the Flash
During Self-
programming
2490G–AVR–03/04
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see Table 124 on page 296), 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 137. Note that the Page Erase
and Page Write operations are addressed independently. Therefore, it is of major impor-
tance that the Boot Loader software addresses the same page in both the Page Erase
and Page Write operation. Once a programming operation is initiated, the address is
latched and the Z-pointer can be used for other operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock
bits. The content of the Z-pointer is ignored and will have no effect on the operation. The
LPM instruction does also use 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 137. Addressing the Flash during SPM
Notes:
Bit
ZH (R31)
ZL (R30)
Z - REGISTER
PROGRAM MEMORY
BIT
1. The different variables used in Figure 137 are listed in Table 114 on page 289.
2. PCPAGE and PCWORD are listed in Table 125 on page 296.
PROGRAM
COUNTER
15
PAGE
Z15
15
Z7
PAGE ADDRESS
WITHIN THE FLASH
7
ZPCMSB
PCMSB
Z14
14
Z6
6
PCPAGE
Z13
Z5
13
5
ZPAGEMSB
PAGEMSB
PCWORD
Z12
12
Z4
4
WORD ADDRESS
WITHIN A PAGE
(1)
1
Z11
Table 2 on page 283
0
0
11
Z3
3
INSTRUCTION WORD
PAGE
Z10
10
Z2
2
ATmega64(L)
Z9
Z1
9
1
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
Z8
Z0
8
0
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