Datasheet

• 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. Please refer to Simple Assembly Code
Example for a Boot Loader for an assembly code example.
28.8.1. 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.
Note: If an interrupt occurs in the timed sequence the four cycle access cannot be guaranteed. In order
to ensure atomic operation disable interrupts before writing to SPMCSR.
28.8.2. 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 page 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.
28.8.3. 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 to 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
Note: If an interrupt occurs in the timed sequence the four cycle access cannot be guaranteed. In order
to ensure atomic operation disable interrupts before writing to SPMCSR.
28.8.4. Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the SPMEN bit
in SPMCR is cleared. This means that the interrupt can be used instead of polling the SPMCR Register in
software. When using the SPM interrupt, the Interrupt Vectors should be moved to the BLS section to
avoid that an interrupt is accessing the RWW section when it is blocked for reading. How to move the
interrupts is described in Interrupts chapter.
Related Links
Atmel ATmega32A [DATASHEET]
Atmel-8155I-ATmega32A_Datasheet_Complete-08/2016
318