Re: MCF5221x Clock Questions

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Hi Mark,
Thank you for the answer.  I am not worried about power in this
case and 48MHz will be plenty of speed.   The MCF52213
is only rated to 50MHz anyway, unlike the 52210 and 52211.
I will probably only be doing an HID implementation of the USB
for this application.

At 12:00 AM 6/22/2008 -0500, [email protected] wrote:
>Message-ID: <[email protected]>
>Date: Sat, 21 Jun 2008 23:31:33 +0200
>From: Mark Butcher <[email protected]>
>To: [email protected]
>Subject: Re: [ColdFire] MCF5221x Clock Questions
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>Content-Transfer-Encoding: 7bit
>Sender: [email protected]
>Reply-To: [email protected]
>
>Bob
>
>The USB can be clocked from the system clock (controlled in 
>USB_CTRL), so a 4MHz input multiplied up to 48MHz is possible. 
>Ensure that the source is 2500ppm accurate to achieve the required 
>precision for full speed USB. I think that the only disadvantage of 
>this is that the system clock can not be used at maximum speed (up 
>to 80MHz otherwise depending on the exact device used).
>By clocking directly from the crystal a 48MHz crystal is needed, but 
>this then doesn't restrict the PLL speed - it could also be reduced 
>to save power in this case.
>
>Regards
>
>Mark Butcher
>
>www.uTasker.com

-Bob
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