Техническая Спецификация для Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI
Модели
MEGA328P-XMINI
256
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
26.
Self-Programming the Flash,
ATmega 48A/48PA
26.1
Overview
In ATmega 48A/48PA there is no Read-While-Write support, and no separate Boot Loader Section. The SPM
instruction can be executed from the entire Flash.
instruction can be executed from the entire Flash.
The device provides a Self-Programming mechanism for downloading and uploading program code by the MCU
itself. The Self-Programming can use any available data interface and associated protocol to read code and
write (program) that code into the Program memory.
itself. The Self-Programming can use any available data interface and associated protocol to read code and
write (program) that code into the Program memory.
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:
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 re-written. 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.
temporary page buffer) before the erase, and then be re-written. 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.
26.1.1 Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “00000011” 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.
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.
The CPU is halted during the Page Erase operation.
Note:
If an interrupt occurs in the time sequence the four cycle access cannot be guaranteed. In order to ensure atomic
operation you should disable interrupts before writing to SPMCSR.
operation you should disable interrupts before writing to SPMCSR.
26.1.2 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 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.
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.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be lost.