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Re: [avr-chat] Trouble with USART0 on ATmega644A

From: David A. Lyons
Subject: Re: [avr-chat] Trouble with USART0 on ATmega644A
Date: Thu, 6 Jan 2011 18:20:06 -0800

On Jan 6, 2011, at 5:49 PM, Rick Mann wrote:
>> Besides defaulting to 8MHz, the factory default 'divide by 8' is set, so 
>> unless you set the fuses, the part is running at 1MHz.
> I think the docs say it's cleared by default. Anyway, I tried both. So, I'm 
> very puzzled that Fosc seems to be 1 MHz.

In <http://www.atmel.com:80/dyn/resources/prod_documents/doc8272.pdf>, I see 
section 8.2.1, "Default Clock Source" saying:

        "The device is shipped with internal RC oscillator at 8.0MHz and with
         the fuse CKDIV8 programmed, resulting in 1.0MHz system clock."

To avoid being misled by fuse documentation elsewhere in the docs, always 
remember that a "programmed" fuse is 0, and an "unprogrammed" fuse is 1.



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