AT90SCR100 datasheet(370/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

28.7

Self-Programming the Flash

The program memory is updated page by page. 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 per word using SPM instruction 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 alter-

native 2 is used, it is not possible to read the old data while loading because 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 374 for an

assembly code example.

28.7.1

Performing Page Erase by SPM

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 are 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.

28.7.2

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 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 be automatically erased 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.

If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be

lost.

AT90SCR100 Datasheet(PDF) 370 Page - ATMEL Corporation

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