Lost connection after FUSE settings change

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Hi Gents,

 

I tried to set up external oscillator to my ATMega1284P. I calculated my FUSE value and wrote to the chip using avrdude.

 

This was the exact command:

avrdude -p m1284p -c atmelice_isp -U lfuse:w:0xf7:m
 

This is the output:

http://mitya.madein.hu/ss/7pDHrv...

 

After it I connected the 20MHz crystal and the 2 x 22pF cap to the XTAL1 and XTAL2 pins, but I am not able to reach the MCU :(

 

http://mitya.madein.hu/ss/BiIh6b...

 

What did I do wrong ? 

Can I get it back ?

 

Thanks,

Mitya

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Classic problem.

 

A crystal is NOT an "oscillator". An "External Oscillator" is a stand-alone device that generates a clock signal whether or not it is connected to a microcontroller. It requires power. Often, then come in a 4-pin metal enclosure. 

 

So, now that you have done this, how do you recover? There are two ways (1) high-voltage programming or (2) connect an external clock source to the XTAL1 pin. This source can be another microcontoller or some other oscillator. You need to know, at least approximately, what the clock frequency is, because your programmer must be set with a clock rate that is slower than 1/4 the frequency of your external oscillator. Once you reset the fuse to one of the "Crystal or Resonator" source types, then you can proceed as normal; your temporary external clock is no longer needed.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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ka7ehk wrote:

Classic problem.

 

A crystal is NOT an "oscillator". An "External Oscillator" is a stand-alone device that generates a clock signal whether or not it is connected to a microcontroller. It requires power. Often, then come in a 4-pin metal enclosure. 

 

Hi Jim,

 

Really sorry, I configured it to have a crystal, I just wrote "external" here, sorry, I need to get used these terms :( These are new for me..

 

So I configured it as it will have a Full swing crystal oscillator (I wrote 011 to CKSEL[3:1])

 

 

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Hmmmmmmmmm

 

I can't believe this, but I connected the crystal to the wrong pins in my breadboard :)

 

http://mitya.madein.hu/ss/0uIhOB...

 

It works :)

 

Thanks anyway, it is good to know about that high voltage solution...

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A crystal is NOT an "oscillator". An "External Oscillator" is a stand-alone device that generates a clock signal whether or not it is connected to a microcontroller

Sorry Jim, you need to get on the hotline & set Atmel straight....they really mucked up their fuse setting names  (corresponds to datasheet "low power crystal"  settings, of course there is also the ext clock)  1-800-avr-guru

 

 

Any wonder users have been locking up their avr's for years??!!...why not have the selections match the datasheet descriptions  (even though, sadly, the datasheets toss "oscillator" into every choice except when possibly actually using an external oscillator..then they call it ext clock)

 

note none of these choices is Ext Crystal Osc !!!!!!!!!!!!!!!!

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Wed. Feb 28, 2018 - 01:41 AM
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I have to tell myself it is the "External Crystal (using the Internal) Oscillator" every time I set fuses...sad

David