[SI-LIST] Re: DDR termination
- From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- To: electronbob2@xxxxxxxxxxxxx
- Date: Thu, 13 May 2004 13:06:05 -0700
Bob
I'd say your final conclusion is on target. DDR termination is rather
"twitchy" to say the least, being a non-perfectly terminated resonant
system. Most consumer motherboards work fine typically, but have
problems with specific memory configurations or corner cases. It is a
safe bet that many of the different memory termination designs that you
see do not work over worst case conditions.
regards,
scott
Bob McNamara wrote:
>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
>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,
>>
>>I would guess that the series termination also
>>varies. Does it?
>>
>>-Chris
>>
>>
>>
>>
>>>-----Original Message-----
>>>From: Bob McNamara
>>>
>>>
>>[mailto:electronbob2@xxxxxxxxxxxxx]
>>
>>
>>>Sent: Thursday, May 13, 2004 11:21 AM
>>>To: 'si-list@xxxxxxxxxxxxx'
>>>Subject: [SI-LIST] DDR termination
>>>
>>>
>>>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.
>>>
>>>Can anybody tell me why there is such a wide
>>>
>>>
>>variation?
>>
>>
>>>Thanks,
>>>
>>>Bob
>>>
>>>
>>>
>------------------------------------------------------------------
>
>
>>>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:
>>
>>
>>>//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:
>>> //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
>>>
>>>
>>>
>>>
>>>
>
>------------------------------------------------------------------
>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:
>//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:
> //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
>
>
>
>
--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC
------------------------------------------------------------------
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:
//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:
//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:
