AT90USB646 Datasheet, PDF (360/434 Pages) ATMEL Corporation – Microcontroller with 64/128K Bytes of ISP Flash and USB Controller

Note: Only one SPM instruction should be active at any time.
28.6
Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers
ZL and ZH in the register file, and RAMPZ in the I/O space. The number of bits actually used is
implementation dependent. Note that the RAMPZ register is only implemented when the pro-
gram space is larger than 64K bytes.
Bit
RAMPZ
ZH (R31)
ZL (R30)
23
15
RAMPZ7
Z15
Z7
7
22
14
RAMPZ6
Z14
Z6
6
21
13
RAMPZ5
Z13
Z5
5
20
12
RAMPZ4
Z12
Z4
4
19
11
RAMPZ3
Z11
Z3
3
18
10
RAMPZ2
Z10
Z2
2
17
9
RAMPZ1
Z9
Z1
1
16
8
RAMPZ0
Z8
Z0
0
Since the Flash is organized in pages (see Table 29-11 on page 373), 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 28-4. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the Boot Loader software
addresses the same page in both the Page Erase and Page Write operation. Once a program-
ming operation is initiated, the address is latched and the Z-pointer can be used for other
operations.
The (E)LPM instruction use the Z-pointer to store the address. Since this instruction addresses
the Flash byte-by-byte, also bit Z0 of the Z-pointer is used.
Figure 28-4. Addressing the Flash During SPM⁽¹⁾
BIT 23
ZPCMSB
ZPAGEMSB 1 0
0 Z - POINTER
PCMSB
PROGRAM COUNTER
PCPAGE
PAGE ADDRESS
WITHIN THE FLASH
PROGRAM MEMORY
PAGE
PAGEMSB
PCWORD
WORD ADDRESS
WITHIN A PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
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