FreeLists / si-list / [SI-LIST] Re: Resistors to use for DDR termination

["Mike Greim" <mike.greim@xxxxxxxxxxx>]

Hi Dimiter,

Unfortunately the answer, as it almost always is,
is it depends.  How many dimms=20
you are supporting on the chanel, supported configurations,
if the design is embedded, etc all impact the termination solution
space.  Simulation is really the answer.  I would also take
care in the design and decoupling of my VTT island as I=20
have seen this be the source of channel failure on a number
of designs.   You also need to figure out how much margin
you are comfortable dealing with.   This will also impact the=20
various length matching requirements you have for the interface.
Leverage your vendor and they may be able to give you an idea
regarding your degrees of flexibility.  They may even be able=20
to simulate a given topology to assess viability.

Let me know if I can be of further assistance.  I just finished=20
fixing one of these interfaces for someone who cut too many=20
corners.

Best Regards,

Michael Greim
Platform Engineering
Newisys, Inc.
512-340-9050, ext 232    (V)
512-740-9097                  (C)

We will either find a way or make one     -Hannibal

And all this science they don't understand
is just my job six days a week........

The time is gone, the email's over
Thought I'd something more to say.......


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx =
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Dimiter Popoff
Sent: Tuesday, July 12, 2005 8:41 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Resistors to use for DDR termination


I am routing a board with an MPC5200 (freescale/mot) which has a
DDR interface (133 MHz clock). What sort of termination resistors =
(resistor arrays?)
do I put? Thera are just so many of them, I begin wondering how
forgiving the 133 MHz interface is and could I get away by just routing
without any terminating restors at <2 inches trace length... I did that
with SDRAM and it worked, now actually I won't be that daring, I cannot
afford a failed board design, it's just the vast number of resistors =
which
brings these thoughts.
 Thanks in advance for the shared experience,

Dimiter

------------------------------------------------------
Dimiter Popoff               Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------

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