5208 and PHY track lengths

Hi,

According the to 5208 data sheet if the length of tracks
from the 5208 to
the PHY are "of significant length" then 22R
resistors should be placed in
series.
Does anyone know what a "significant length" is
?
Our total track length is 70mm.
If we need to add resistors should they be placed closer to
the 5208 or
closer to the phy or doesn't it matter ?

Thanks
Paul




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Paul,

You should place the resistor close to the driver side of
the trace in 
question.  Since it's a PHY, you'll probably be using an
MII interface?  
In that case, some of the resistors will go near the PHY and
others 
closer to the Coldfire, depending on  the direction of the
drive.

"significant length" refers to whether the trace
is long enough to 
encourage ringing and/or reflections.  The max length of the
trace 
depends on the rise time of the output driver, and the speed
of 
propagation of the signal down the trace.  If in doubt over
the length, 
you could probably just install the resistors.

Also, I recommend purchasing some books on high speed PCB
design:

***
High Speed Digital Design - A Handbook of Black Magic
Howard Johnson, Martin Graham
1993 Prentice Hall
***

Printed Circuit Board Design Techniques for EMC Compliance
Mark Montrose
IEEE Press

Printed Circuit Design
Gerald Ginsberg
1991 McGraw-Hill


Cheers,
Aaron Shepard


parnoldbellfruitgames.co.uk wrote:

>Hi,
>
>According the to 5208 data sheet if the length of tracks
from the 5208 to
>the PHY are "of significant length" then 22R
resistors should be placed in
>series.
>Does anyone know what a "significant length"
is ?
>Our total track length is 70mm.
>If we need to add resistors should they be placed closer
to the 5208 or
>closer to the phy or doesn't it matter ?
>
>Thanks
>Paul
>
>
>
>
>________________________________________________________
________________
>DISCLAIMER:
>
>Information contained in this email or any attachment
may be of a
>confidential nature which should not be disclosed to,
copied or used by
>anyone other than the addressee. It may also be legally
privileged.
>If you receive this email in error, please delete the
email from your computer and notify the sender immediately
by return E-mail.
>
>Security Warning: Please note that this email has been
created in the knowledge that Internet email is not a 100%
secure communications medium.  
>
>Virus Warning:
>This email has been scanned for all viruses by
MessageLabs.
>Although this email and any attachment are believed to
be
>free from viruses, it is the responsibility of the
recipient to ensure that
>they are virus free. No responsibility is accepted by
Bell-Fruit Games Ltd
>for any loss or damage arising in any way from their
receipt, opening or
>use.
>--------------------------------------------------------
------------
>To Subscribe send a message to:      ColdFire-OnLists.Wildrice.com
>To Unsubscribe send a message to:    ColdFire-OffLists.Wildrice.com
>For further information, visit:      <http://www.Wild
Rice.com/ColdFire/>
>
>  
>

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