Burning code at one voltage and running at another. OK?

Other Hardware 3rd Party Boards
1

Hi all,

Quick question: If I burn a bootloader or code (actually, anything) to an AVR device at Vdd=3.3 but run the chip at Vdd=5.0, will the flash still be reliable?

2

(deleted)

3

spycatcher2k:
Yes - IF it's a 5V tolerant chip. I do this a lot as my programmer is set at 3.3V

Thanks! Yes the chips are 5v (mega328p, mega2560, etc..)

4

Mega2560 is not a 3.3V chip, datasheet says it needs 4.5V to 5.5V at any frequency.

5

CrossRoads:
Mega2560 is not a 3.3V chip, datasheet says it needs 4.5V to 5.5V at any frequency.

That is very interesting. I never realized that! I've been using a 2560 with two AAA lithium cells at 16 MHz successfully although it seems that I have only been lucky.

The very first page of the datasheet says:

Speed Grade:
– ATmega640V/ATmega1280V/ATmega1281V:
    • 0 - 4MHz @ 1.8V - 5.5V, 0 - 8MHz @ 2.7V - 5.5V
– ATmega2560V/ATmega2561V:
    • 0 - 2MHz @ 1.8V - 5.5V, 0 - 8MHz @ 2.7V - 5.5V
– ATmega640/ATmega1280/ATmega1281:
    • 0 - 8MHz @ 2.7V - 5.5V, 0 - 16MHz @ 4.5V - 5.5V
[color=red][b]– ATmega2560/ATmega2561:
    • 0 - 16MHz @ 4.5V - 5.5V[/b]

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... and near the end:

(click for larger)
2560.jpg

How I missed both is beyond me.