[SI-LIST] Re: DDR-2 DQS

  • From: "John Ellis" <jellis@xxxxxxxxx>
  • To: <swldstn@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 14 Oct 2003 17:44:48 -0400

Hi Steve,

As I understand the spec, these are differential strobes with timing
referenced to the zero crossing of the true and complement.  This is how
TriCN implements the DDR 2 strobe in our IP.  Jedec's most recently released
document muddied the waters a bit when they revised the pindescription to
say

"... The data strobes DQS, LDQS, UDQS, and RDQS may be used in single
ended mode or paired with optional complementary signals DQS, LDQS,
UDQS, and RDQS to
provide differential pair signaling to the system during both reads and
writes...."

The spec used to just refer to a "differential strobe" which is certainly
more clear.

Complementary signaling, at least as I define it, is found in the RLDRAM
specs which are modeled after QDR SRAM specs.  Here the timing of the DQ is
measured to the rising edges of the DQS and DQS# ( Or K and K# with SRAMs).
DQS and DQS# are treated as separate strobes, nominally 180 degrees out of
phase in complementary signaling.

Hope this helps.

John Ellis

Vice President
Interconnect Technology

TriCN, Inc.

3605 Vartan Way
Suite 301
Harrisburg, PA  17110

Phone:717-657-1002
Fax:  717-221-1185
email:jellis@xxxxxxxxx

www.tricn.com

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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Steven M. Waldstein
Sent: Monday, October 13, 2003 7:35 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] DDR-2 DQS


Now that I see that DDR-2 questions are being asked
I've got mine to ask.

On the current DDR-2 specifications they show
"differential" DQS as an improvement to improve timing
accuracy. Can anyone tell me if these are really
"differential driver and/or receivers" on the memories or
are these really complimentary strobes?

My reason for asking is that the I often see them referred
to as differential but the terminations appear to more
representative of a complimentary implementations.

Also, most of the IP available from vendors to implement
the controller are complementary implementations. I want to
make sure these are the proper implementation.

Any personal experience would be helpful. Thanks in advance.

Steve Waldstein
swldstn@xxxxxxxxxxxx



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