Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet

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ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]

Atmel-8271H-AVR- ATmega-Datasheet_08/2014

Note that the RWWSB bit will always be read as zero in ATmega 48A/48PA. Nevertheless, it is recommended to 
check this bit as shown in the code example, to ensure compatibility with devices supporting Read-While-Write.

;-the routine writes one page of data from RAM to Flash

; the first data location in RAM is pointed to by the Y pointer

; the first data location in Flash is pointed to by the Z-pointer

;-error handling is not included

;-the routine must be placed inside the Boot space

; (at least the Do_spm sub routine). Only code inside NRWW section can

; be read during Self-Programming (Page Erase and Page Write).

;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24), 

; loophi (r25), spmcrval (r20)

; storing and restoring of registers is not included in the routine

; register usage can be optimized at the expense of code size

;-It is assumed that either the interrupt table is moved to the Boot

; loader section or that the interrupts are disabled.

.equ

PAGESIZEB = PAGESIZE*2;PAGESIZEB is page size in BYTES, not 

words

.org SMALLBOOTSTART

Write_page:

;

Page Erase

ldi

spmcrval, (1<<PGERS) | (1<<SPMEN)

rcall

Do_spm

;

re-enable the RWW section

ldi

spmcrval, (1<<RWWSRE) | (1<<SPMEN)

rcall

Do_spm

;

transfer data from RAM to Flash page buffer

ldi

looplo, low(PAGESIZEB);init loop variable

ldi

loophi, high(PAGESIZEB);not required for 

PAGESIZEB<=256

Wrloop:

ld

r0, Y+

ld

r1, Y+

ldi

spmcrval, (1<<SPMEN)

rcall

Do_spm

adiw

ZH:ZL, 2

sbiw

loophi:looplo, 2;use subi for PAGESIZEB<=256

brne

Wrloop

;

execute Page Write

subi

ZL, low(PAGESIZEB);restore pointer

sbci

ZH, high(PAGESIZEB);not required for PAGESIZEB<=256

ldi

spmcrval, (1<<PGWRT) | (1<<SPMEN)

rcall

Do_spm

;

re-enable the RWW section

ldi

spmcrval, (1<<RWWSRE) | (1<<SPMEN)

rcall

Do_spm