ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 329

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Performing Page Erase by
SPM
Filling the Temporary Buffer
(Page Loading)
Performing a Page Write
Using the SPM Interrupt
2549K–AVR–01/07
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 333 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 will be ignored 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 tempo-
rary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded
is still buffered.
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 to zero during this operation.
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If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt
when the SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used
instead of polling the SPMCSR Register in software. When using the SPM interrupt, the
Interrupt Vectors should be moved to the BLS section to avoid that an interrupt is
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.
ATmega640/1280/1281/2560/2561
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