User guide

223
ATmega162/V
2513E–AVR–09/03
Self-programming the
Flash
The program memory is updated in a page by page fashion. Before programming a
page with the data stored in the temporary page buffer, the page must be erased. The
temporary page buffer is filled one word at a time using SPM and the buffer can be filled
either before the Page Erase command or between a Page Erase and a Page Write
operation:
Alternative 1, fill the buffer before a Page Erase
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
Alternative 2, fill the buffer after Page Erase
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for
example in the temporary page buffer) before the erase, and then be rewritten. When
using alternative 1, the Boot Loader provides an effective Read-Modify-Write feature
which allows the user software to first read the page, do the necessary changes, and
then write back the modified data. If alternative 2 is used, it is not possible to read the
old data while loading since the page is already erased. The temporary page buffer can
be accessed in a random sequence. It is essential that the page address used in both
the Page Erase and Page Write operation is addressing the same page. See “Simple
Assembly Code Example for a Boot Loader” on page 226 for an assembly code
example.
Performing Page Erase by
SPM
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to
SPMCR and execute SPM within four clock cycles after writing SPMCR. The data in R1
and R0 is ignored. The page address must be written to PCPAGE in the Z-register.
Other bits in the Z-pointer will be ignored during this operation.
• Page Erase to the RWW section: The NRWW section can be read during the Page
Erase.
• Page Erase to the NRWW section: The CPU is halted during the operation.
Filling the Temporary Buffer
(Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCR and execute SPM within four clock cycles after writing SPMCR.
The content of PCWORD in the Z-register is used to address the data in the temporary
buffer. The temporary buffer will auto-erase after a Page Write operation or by writing
the RWWSRE bit in SPMCR. It is also erased after a System Reset. Note that it is not
possible to write more than one time to each address without erasing the temporary
buffer.
Note: If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded
will be lost.
Performing a Page Write To execute Page Write, set up the address in the Z-pointer, write “X0000101” to
SPMCR and execute SPM within four clock cycles after writing SPMCR. 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 zero during this operation.
• Page Write to the RWW section: The NRWW section can be read during the Page
Write.
• Page Write to the NRWW section: The CPU is halted during the operation.