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
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
RAMPZ
ZH (R31)
ZL (R30)
RAMPZ7
RAMPZ6
RAMPZ5
RAMPZ4
RAMPZ3
RAMPZ2
RAMPZ1
RAMPZ0
Z15
Z7
7
Z14
Z6
6
Z13
Z5
5
Z12
Z4
4
Z11
Z3
3
Z10
Z2
2
Z9
Z1
1
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
PAGEMSB
PROGRAM COUNTER
PCPAGE
PCWORD
PAGE ADDRESS
WITHIN THE FLASH
WORD ADDRESS
WITHIN A PAGE
PROGRAM MEMORY
PAGE
PAGE
INSTRUCTION WORD
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
360
AT90USB64/128
7593A–AVR–02/06
ATMEL [ ATMEL ]
