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

From: Rick Mann
Subject: Re: [avr-chat] Trouble with USART0 on ATmega644A
Date: Thu, 6 Jan 2011 17:49:40 -0800

On Jan 6, 2011, at 09:17:14, Bill Rochat 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.

> At 8MHz, the best baud rate accuracy you can get is -3.5% on 2x operaion, 
> which is very marginal to say the least.  Also, the 8MHz internal oscillator 
> will not be exact, and may be off 1.5% give or take.  

I could swear I succeeded before at that speed (at 1 MHz!), but I must be 
wrong. I'll look for a more accurate speed, or try Joerg's suggestion to adjust 
the internal oscillator.


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