ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 284

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

Self-programming the
Flash
Performing Page Erase by
SPM
Filling the Temporary Buffer
(Page Loading)
Performing a Page Write
284
ATmega64(L)
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:
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Alternative 2, fill the buffer after Page Erase:
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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 287 for an assembly code
example.
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” 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 in the Z-register.
Other bits in the Z-pointer must be written zero during this operation.
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To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCSR and execute SPM within four clock cycles after writing
SPMCSR. 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 SPMCSR. 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:
To execute Page Write, set up the address in the Z-pointer, write “X0000101” 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 zero during this operation.
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Fill temporary page buffer
Perform a Page Erase
Perform a Page Write
Perform a Page Erase
Fill temporary page buffer
Perform a Page Write
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.
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.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded
will be lost.
2490G–AVR–03/04