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Author Topic: Got the internal oscillator working can't use 3.3v  (Read 698 times)
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I was able to get an Atmega328p (DIP) working with the internal oscillator at 8mhz using a 5v supply, but now it won't run at 3.3v. I'm wondering if I neglected something with my fuse settings, since I've been able to boot 16mhz *duino boards at 3.3v in the past... Or, maybe some weird shenanigans because the firmware is made for the surface mount 'megas...?

My fuse settings and bootloader:
    low fuses: 0xF2
    high fuses: 0xDA
    extended fuses: 0x05
    bootloader: ATmegaBOOT_168_atmega328_pro_8MHz.hex

Thanks for the help

EDIT:
I just figured I'd copy the old revision '168-based Lilypad's fuse bits and now it runs fine. (Though if you notice I'm doing something bad with the fuses, tell me smiley-wink )
    low fuses: 0xE2
    high fuses: 0xDD
    extended fuses: 0x00
    bootloader: ATmegaBOOT_168_atmega328_pro_8MHz.hex

Does anyone know where a nice fuse diagram for the 'megas (including the extended byte) is, and if the '168 and '328 fuse settings are the same? (it seems so from the datasheet I have...)
« Last Edit: January 04, 2010, 01:54:18 pm by gbpic » Logged

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I don't see anything obviously wrong with the fuse settings.

I use the fuse calculator here...
http://www.engbedded.com/fusecalc/

There's also one here...
http://frank.circleofcurrent.com/fusecalc/fusecalc.php

...that was announced here...
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1261451556/2
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Though if you notice I'm doing something bad with the fuses, tell me
You need to change brown out detetcion (BOD) level. The fuse settings you listed set the level at 4.3V and so the mcu will never come alive at 3.3V.
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extended fuses: 0x05

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You need to change brown out detetcion (BOD) level. The fuse settings you listed set the level at 4.3V and so the mcu will never come alive at 3.3V.

According to this fuse calculator...
http://www.engbedded.com/fusecalc/

...the BOD level would be 2.7 volts.  Did I misinterpret what the calculator is showing?
 

The original fuse settings are for "external clock" which is not the same as "external oscillator".  Are you trying to run from the internal oscillator or from an external one?
« Last Edit: January 05, 2010, 02:02:25 am by bcook » Logged

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If you look further down he specifies:

Extended fuses: 0x00

This would leave BOD at 4.3V. He writes that this configuration is working (I assume at 3.3V), but this doesn't make sense. Rather it is reasonable to assume that he got the fuse settings mixed up somehow. The issue reported is consistent with an incorrect BOD setting (works at 5V, doesn't work at 3V3).  

Figuring out fuse settings from the datasheet only is a hassle (using inverse logic) - using the Engbedded calculator makes it a lot easier.

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Yes, I did have to change my BOT to a lower value. My new fuses are:

low: E2
high: DA
extended: 06
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Just a few questions regarding this:
I want to use the internal osci too, cause i want to fit a cell phone into a old-schools telephone... (and do need 3,3V to use)

I want to use the ArduinoISP-sketch. (i did succesfully burn some 328p...with 16MHz crystal)

If i setup the target 328. Do i need an oscillator (or crystal and Cs) on it?
Or can i leave out the two pins? Or need to tie high/low?

And:

I read, that the internal osci is quite unstable.
So: How unstable is it? Will i get serialconnection to work?
(i'm not sure how precise the timings have to be....)


Thanks in advance. smiley


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