MCF5221x Clock Questions

[Robert Ritchey]

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Hi,
I am just switching into the Coldfire line and am using the MCF51QE32 and
the MCF52213 in new designs.  The details for using a crystal or resonator
with the MCF51QE32 are detailed very nicely in the data sheet.  On the other
hand there is virtually no information in the MCF5221x data sheet or reference
manual about how to hook up a crystal or resonator.  I would like to use a
4MHz resonator with this part and the PLL to boost this to 48MHz internal.

A second question about the MCF5221x parts regarding the 48MHz for the
USB.  Do I have to use a 48MHz crystal for some reason or can I use the
PLL output at 48MHz?  The diagram looks like I can use the PLL but my
Arrow FAE for Coldfire said he was told I needed a 48MHz crystal.

Thanks for any help in advance.

-Bob
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Robert Ritchey
Quest Engineering & Development, Inc.
Suite B/8
6125 South Ash Avenue
Tempe, AZ 85283
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[Mark Butcher]

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

>
> Hi,
> I am just switching into the Coldfire line and am using the MCF51QE32 and
> the MCF52213 in new designs.  The details for using a crystal or
> resonator
> with the MCF51QE32 are detailed very nicely in the data sheet.  On the
> other
> hand there is virtually no information in the MCF5221x data sheet or
> reference
> manual about how to hook up a crystal or resonator.  I would like to
> use a
> 4MHz resonator with this part and the PLL to boost this to 48MHz
> internal.
>
> A second question about the MCF5221x parts regarding the 48MHz for the
> USB.  Do I have to use a 48MHz crystal for some reason or can I use the
> PLL output at 48MHz?  The diagram looks like I can use the PLL but my
> Arrow FAE for Coldfire said he was told I needed a 48MHz crystal.
>
> Thanks for any help in advance.
>
> -Bob
> --------------------------------------------------------------------
> Robert Ritchey
> Quest Engineering & Development, Inc.
> Suite B/8
> 6125 South Ash Avenue
> Tempe, AZ 85283
> Tel: [phone]
> FAX: [phone]
> E-Mail: RRRitchey@...
> E-Mail: RRRitchey@...
> E-Mail: RRRitchey@...
> E-Mail: RRRitchey@...
> WWW: www.QuestEngDev.com/
> WWW: www.Smart-Fly.com/
> --------------------------------------------------------------------
> ---
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[Robert Ritchey]

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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, coldfire@... wrote:

>Message-ID: <485D7335.9080800@...>
>Date: Sat, 21 Jun 2008 23:31:33 +0200
>From: Mark Butcher <Mark@...>
>To: coldfire@...
>Subject: Re: [ColdFire] MCF5221x Clock Questions
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>Content-Transfer-Encoding: 7bit
>Sender: coldfire-bounce@...
>Reply-To: coldfire@...
>
>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
--------------------------------------------------------------------
Robert Ritchey
Quest Engineering & Development, Inc.
Suite B/8
6125 South Ash Avenue
Tempe, AZ 85283
Tel: [phone]
FAX: [phone]
E-Mail: RRRitchey@...
E-Mail: RRRitchey@...
E-Mail: RRRitchey@...
E-Mail: RRRitchey@...
WWW: www.QuestEngDev.com/
WWW: www.Smart-Fly.com/
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[John Bodnar]

Robert Ritchey wrote:
> A second question about the MCF5221x parts regarding the 48MHz for the
> USB.  Do I have to use a 48MHz crystal for some reason or can I use the
> PLL output at 48MHz?  The diagram looks like I can use the PLL but my
> Arrow FAE for Coldfire said he was told I needed a 48MHz crystal.

Your Arrow FAE is correct, you must use a 48 MHz fundamental mode crystal.

The PLL jitter specification is too high to meet the 2500 ppm USB
full-speed clock jitter specification.

We intend for the USB clock to be derived directly from the 48 MHz
crystal or from the USB_ALTCLK bypass input.

USB will likely work when using the system clock, but whether it does so
consistently depends on how tolerant whatever you plug into actually is.

John Bodnar
Systems Engineer
Freescale Semiconductor, Inc.
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[Mark Butcher]

Hi John

Rich T has used the USB driven from the relaxation oscillator (!!!) -
see
http://forums.freescale.com/freescale/board/message?board.id=CFCOMM&thread.id=4734
but as he also comments, the accuracy (and jitter (?)) is not within
spec., so obviously not recommended....

Regards

Mark

http://www.uTasker.com

> Robert Ritchey wrote:
>> A second question about the MCF5221x parts regarding the 48MHz for the
>> USB.  Do I have to use a 48MHz crystal for some reason or can I use the
>> PLL output at 48MHz?  The diagram looks like I can use the PLL but my
>> Arrow FAE for Coldfire said he was told I needed a 48MHz crystal.
>
> Your Arrow FAE is correct, you must use a 48 MHz fundamental mode
> crystal.
>
> The PLL jitter specification is too high to meet the 2500 ppm USB
> full-speed clock jitter specification.
>
> We intend for the USB clock to be derived directly from the 48 MHz
> crystal or from the USB_ALTCLK bypass input.
>
> USB will likely work when using the system clock, but whether it does
> so consistently depends on how tolerant whatever you plug into
> actually is.
>
> John Bodnar
> Systems Engineer
> Freescale Semiconductor, Inc.
> ---
>
>
>

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