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Microcontroller Programming » oscillator fuse bits

December 22, 2012
by eminthepooh
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Hey guys, I set the fuse bits of a couple of my m168's to use the low power crystal oscillator and now they won't talk back. I made sure the SPI fuse bit wasn't touched. I had a dinky 8Mhz crystal sort of like the one in the nerdskit hooked up (which is what I thought a low power oscillator is)

After reading through the nerdkit's fuses I saw that it comes programmed with the full swing fuse set, I tried that and it works.

Can someone help me get my other two m168's that still think they should be getting a low power oscillator on them fixed? They are programmed with 0x64, 0xdf, 0xf9 fuses.

Thank you,

December 22, 2012
by Noter
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Did you try them with the regular 14.7456MHz crystal that comes with the nerdkit? I think the low power oscillator is more for power saving than requiring a different type of crystal. See if you can set the fuses back to their original values using that crystal. Also I like to use an online fuse calculator like http://www.engbedded.com/fusecalc, it's easier than reading the datasheet.

December 22, 2012
by eminthepooh
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I did use the act fuse calculator. The 8mhz crystal I got is same as the 14.7456mhz that came with the kit. Plus the chip came with the full swing fuse programmed. So I would assume wherever the 14mhz works so does my 8mhz. I still don't get why the low power won't work and the full swing will :(

December 22, 2012
by Noter
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I took a look on the web and found the low power crystal needed is a ~32khz watch crystal. So I guess you'll have to get one of those to recover those chips. If you have access to a a high voltage parallel programmer you could reset the fuses with that too. I think they are a little on the expensive side though.

watch crystal

December 22, 2012
by Noter
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Forgot to answer your other question -

If you look at the datasheet on the atmega168 it says the full swing crystal operates VCC to GND which is a 5v swing. I don't remember the voltage swing for the low power crystal but it isn't enough to get a full swing crystal oscillating.

December 22, 2012
by eminthepooh
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Thanks Noter, I'll try the slower crystals.

December 23, 2012
by Ralphxyz
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If you have access to a a high voltage parallel programmer you could reset the fuses with that too. I think they are a little on the expensive side though.

The Atmel Dragon does parrallel programing for $49.00.

This biggest problem with the Dragon is that it is just a populated PCB no case so you might set down on wire on your desktop and short it out.

Ralph

December 23, 2012
by eminthepooh
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Yeah I wasn't too excited about parallel programmers. All I know about them is that they can bring your bricked micros back to life. Crystals are a dollar and my two bricked micros are $3 together so I'd rather just buy new micros.

Thanks guys

December 24, 2012
by Ralphxyz
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I use my Dragon in parallel mode as much as I use my Nerdkit USB maybe even more.

There is no challenge to using parallel mode except YOU can mess up the fuse setting greater than with ISP, of course you can also do ISP with the Dragon.

Plus, if one ever gets around to learning how, you can do on-chip debugging (with certain chips).

Ralph

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