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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 19:46:01 -0800 |
On Jan 6, 2011, at 18:20:06, David A. Lyons wrote:
> 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.
Yep, I'm quite familiar with "programmed" meaning 0. But that is not the same
as saying that "programmed/0" means "this feature enabled." Does it? I'm never
sure. A "1" usually means a feature is enabled (otherwise things are
active-low, and have a bar over them ;-) ).
--
Rick