[SI-LIST] Re: DDR SDRAM signal routing
- From: Ed Sayre III <esayre3@xxxxxxxx>
- To: pm_norge@xxxxxxxxxxx
- Date: Mon, 08 Nov 2004 12:32:51 -0500
Peter,
You NEED to run simulations. I have worked on DDR SDRAMs architectures
for many years now and every one was slightly different. You can benefit
greatly from simulations since it generates your skew budget, component
placement and proper termination among other design points. If you
management tells you that they are willing to spend the money on repeated
turns, where you may or may not find the right answer, then you are wasting
your money. Either hire a consultant with experience in the area of DDR
memory or develop your own in house expertise. There are many people and
products available right now. The driving force behind all this is time
to market and system reliability.
Good luck
-Ed Sayre
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NORTH EAST SYSTEMS ASSOCIATES, INC
-------------------------------------
"High Performance Engineering & Design"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Edward Sayre 3rd e-mail: esayre3@xxxxxxxx
NESA, Inc. http://www.nesa.com/
5 Lan Drive, Suite 200 Tel +1.978.392-8787 x 218
Westford, MA 01886 USA Fax +1.978.392-8686
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At 09:32 AM 11/8/2004 +0000, you wrote:
>I have been designing different kinds of electronic products, but never a
>DDR SDRAM interface with 16 memory chips (MT46V64M8, 512Mb chip, 8-bit @
>167MHz)and 2 ECC chips (same type).
>
>Between the processor (IBM PowerPC 440GX) and memory chips there are only
>the transmission lines and series termination resistors (25Ohm close to the
>processor). I do not have the possibility to run simulations, so it's
>learning by doing.
>
>The data lines are around 60-70mm and the address line around 250mm!!! long.
>I'm afraid I will get serious SI problems with this configuration. I read
>some Appnotes but I could really use some help from experienced SI
>designers. What kind of termination do I really have to implement and what
>do I have to look out for?
>
>Thanks in advance
>Peter
>
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