Author Topic: Setting ATMEGA8 to 8Mhz  (Read 5755 times)

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Offline richiereynoldsTopic starter

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Setting ATMEGA8 to 8Mhz
« on: February 05, 2010, 03:35:54 AM »
Hi There! this is my first post.

I made the $50 robot, added scanning and made up my own obstacle avoidance and "stay on a table" alogorithms, all worked great, very happy, until ...

Was going to add some uart functionality so wanted to up my processing speed from 1Mhz to 8Mhz following the uart tutorial. I'm using the avr studio version shown on the $50 robot page with SP1 and SP2 installed and the AVRISP Mk11 programmer. However, on the fuse programming tab the options I have are different to those shown in the tutorial. There's no "divisor by 8" and long list of checkboxes with the processing speeds, just a dropdown for CKSEL fuses.
I guessed that the divde by 8 bit is for another processor so I ignored that.
On the dropdown I selected "Int RC Osc. 8 MHz; Start-up time: 6 CK + 64 ms; [CKSEL-0101 SUT=10]"
Firstly, can anyone confirmt that I have chosen the right options and that's all I need to do?

I hit program and it did program the fuses, but obviosuly it programmed them wrongly and now I'm locked out of my chip, "Failed to enter Programming Mode ...".

Has anyone done this using this AVR studio version?

Thanks all!
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Offline Admin

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Re: Setting ATMEGA8 to 8Mhz
« Reply #1 on: February 08, 2010, 12:58:46 AM »
Sorry, AVR Studio re-did the GUI and the tutorial was never updated.

What you ended up doing is telling the AVR to use an external crystal. To fix it, you need two capacitors and a crystal:
http://www.societyofrobots.com/microcontroller_xtal.shtml

Or just buy a new microcontroller :P

The advantage of the crystal is you can bump up the processing speed even higher. Faster UART, faster processing, etc.

The divide by 8 bit fuse was the one you wanted to uncheck. (when checked the clock is divided by 8, making it 8 times slower)
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Offline richiereynoldsTopic starter

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Re: Setting ATMEGA8 to 8Mhz
« Reply #2 on: February 08, 2010, 03:23:00 PM »
Cheers, actually picked up a couple of atmega328p chips on ebay, when they arrived I couldn't program them either but added an 8MHz 3 pin ceramic resonator and voila, was up and running. Set them both to 8Mhz internal clock without the divisor and away we go! No more need for the resonator.

Tried the same resonator with the atmega8 I had toasted but no luck, no idea what way I've got that programmed!
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