attiny25v ATMEL Corporation, attiny25v Datasheet - Page 146

• Manufacturer Part Number: attiny25v
• Description: Microcontroller With 2/4/8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

19.3
19.4
146
Performing a Page Write
Addressing the Flash During Self-Programming
ATtiny25/45/85
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
To execute Page Write, set up the address in the Z-pointer, write “00000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to
zero during this operation.
Note:
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see
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
addressed independently. Therefore it is of major importance that the software addresses the
same page in both the Page Erase and Page Write operation.
The LPM instruction uses 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 19-1. Addressing the Flash During SPM
Note:
Bit
ZH (R31)
ZL (R30)
Z - REGISTER
The CPU is halted during the Page Write operation.
1. The different variables used in
PROGRAM MEMORY
BIT
15
Z15
Z7
7
PAGE
PROGRAM
COUNTER
15
Figure
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
14
Z14
Z6
6
PCMSB
19-1. Note that the Page Erase and Page Write operations are
PCPAGE
13
Z13
Z5
5
Figure 19-1
ZPAGEMSB
12
Z12
Z4
4
PAGEMSB
Table 20-8 on page
PCWORD
WORD ADDRESS
WITHIN A PAGE
(1)
are listed in
11
Z3
3
Z11
1
0
0
INSTRUCTION WORD
10
Z10
Z2
2
PAGE
Table 20-8 on page
154), the Program Counter can
9
Z9
Z1
1
PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
8
Z8
Z0
0
154.
2586K–AVR–01/08