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

During periods of low V

CC

, the Flash program can be corrupted because the supply voltage is too low for the 

CPU and the Flash to operate properly. These issues are the same as for board level systems using the Flash, 
and the same design solutions should be applied. 

A Flash program corruption can be caused by two situations when the voltage is too low. First, a regular write 
sequence to the Flash requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute 
instructions incorrectly, if the supply voltage for executing instructions is too low.

Flash corruption can easily be avoided by following these design recommendations (one is sufficient):

1. If there is no need for a Boot Loader update in the system, program the Boot Loader Lock bits to prevent 

any Boot Loader software updates.

2.

Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done 
by enabling the internal Brown-out Detector (BOD) if the operating voltage matches the detection level. If 
not, an external low V

CC

 reset protection circuit can be used. If a reset occurs while a write operation is in 

progress, the write operation will be completed provided that the power supply voltage is sufficient.

3.

Keep the AVR core in Power-down sleep mode during periods of low V

CC

. This will prevent the CPU from 

attempting to decode and execute instructions, effectively protecting the SPMCSR Register and thus the 
Flash from unintentional writes.

The calibrated RC Oscillator is used to time Flash accesses. 

 shows the typical programming time for 

Flash accesses from the CPU.

Note:

1.

Minimum and maximum programming time is per individual operation.

;-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)

call

Do_spm

Flash write (Page Erase, Page Write, and 
write Lock bits by SPM)

3.7ms

4.5ms