[SI-LIST] Re: DDR termination

I have seen a lot of instances where the interfaces
are designed by using data suggested in the chip
manufacturers literature buffered in experience.  Many
times a design of a mother board will never be seen by
someone who knows what signal integrity analysis
really is.

David Lieby
Siemens Medical Solutions, Ultrasound Division
Mountain View, CA

--- "Brown, Mike (Austin, TX)" <mibrown@xxxxxx> wrote:
> I think you have nailed it:=20
> 
> "It seems to me that the only other possibility is
> that some of these =
> manufacturers didn't do their homework, and their
> memory system designs =
> are marginal."
> 
> Another possibility is that they have used a
> different routing topology =
> for some reason and have tweaked their termination
> to suit.  I refer you =
> to the above paragraph.
> 
> Mike
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
> Bob McNamara
> Sent: Thursday, May 13, 2004 2:09 PM
> To: Chris McGrath
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: DDR termination
> 
> 
> It's really all over the map, even with motherboards
> using the same chipset.  Some have no series term,
> others have 10 Ohm or 22 Ohm.  The parallel terms
> vary from 27 Ohm up to 68 Ohm.  Some use no series
> term for address/command and have a small cap to
> ground.  Others have artwork for the cap but it's
> not stuffed.
> 
> I think one motherboard had no series term and a
> 33 Ohm parallel term, while another (using the
> same chipset and claiming the same memory speeds)
> had no series term and a 68 Ohm parallel term.
> 
> I would have thought that for a given chipset, there
> would be some combination of resistor values that
> would produce the best signal integrity.  If I make
> the rash assumption that all of these
> implementations
> work equally well, my conclusion is that the value
> of the parallel termination isn't particularly=20
> critical.
> 
> It seems to me that the only other possibility is
> that some of these manufacturers didn't do their
> homework, and their memory system designs are
> marginal.
> 
> Bob
> 
> --- Chris McGrath <chris.mcgrath@xxxxxxxx> wrote:
> > Bob,
> >=20
> > I would guess that the series termination also
> > varies.  Does it?
> >=20
> > -Chris
> >=20
> >=20
> > > -----Original Message-----
> > > From: Bob McNamara
> > [mailto:electronbob2@xxxxxxxxxxxxx]=20
> > > Sent: Thursday, May 13, 2004 11:21 AM
> > > To: 'si-list@xxxxxxxxxxxxx'
> > > Subject: [SI-LIST] DDR termination
> > >=20
> > >=20
> > > I was looking over motherboards at Fry's
> yesterday
> > and
> > > noticed quite a wide variation in the resistor
> > values
> > > used for parallel termination: 27, 33, and 56.
> > >=20
> > > Can anybody tell me why there is such a wide
> > variation?
> > >=20
> > > Thanks,
> > >=20
> > > Bob
> > >
> >
>
------------------------------------------------------------------
> > > To unsubscribe from si-list:
> > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe'
> > in the Subject field
> > >=20
> > > or to administer your membership from a web
> page,
> > go to:=20
> > > http://www.freelists.org/webpage/si-list
> > >=20
> > > For help:
> > >=20
> > > si-list-request@xxxxxxxxxxxxx with 'help' in the
> > Subject field
> > >=20
> > > List FAQ wiki page is located at:
> > >               =20
> > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> > >=20
> > > List technical documents are available at:
> > >                 http://www.si-list.org
> > >=20
> > > List archives are viewable at:    =20
> > >           http://www.freelists.org/archives/si-list
> > > or at our remote archives:
> > >           http://groups.yahoo.com/group/si-list/messages
> > > Old (prior to June 6, 2001) list archives are
> > viewable at:
> > >           http://www.qsl.net/wb6tpu
> > >  =20
> > >=20
> > >=20
> 
>
------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in
> the Subject field
> 
> or to administer your membership from a web page, go
> to:
> http://www.freelists.org/webpage/si-list
> 
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the
> Subject field
> 
> List FAQ wiki page is located at:
>                
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> 
> List technical documents are available at:
>                 http://www.si-list.org
> 
> List archives are viewable at:    =20
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are
> viewable at:
>               http://www.qsl.net/wb6tpu
>  =20
> 
>
------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in
> the Subject field
> 
> or to administer your membership from a web page, go
> to:
> http://www.freelists.org/webpage/si-list
> 
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the
> Subject field
> 
> List FAQ wiki page is located at:
>                
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> 
> List technical documents are available at:
>                 http://www.si-list.org
> 
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are
> viewable at:
>               http://www.qsl.net/wb6tpu
>   
> 


        
                
__________________________________
Do you Yahoo!?
SBC Yahoo! - Internet access at a great low price.
http://promo.yahoo.com/sbc/
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: