[SI-LIST] Re: DDR-1 termination (short point-to-point)

Kristiaan, SSN can be a challenge with big FPGA packages and large parallel 
busses.  It is important to plan the pin assignments so that the crosstalk 
/ SSO does not blow the timing budget, or subject the chip I/O to excess 
voltage swing.  The Xilinx ISE tools do not provide SSO, or in-package PDS 
droop information.

You are corect that V2P inputs really need to be held to 3V absolute, or 
device life will be shortened.  The devil with DCI is that it alters the 
timing and will limit the speed at which a V2P DDR interface can 
run.  Xilinx' reference designs call for DCI disabled with DDR on V2, and V2P.

Regards,


Steve.
At 12:25 AM 2/6/2005 +0100, De Paepe, Kristiaan wrote:
>Julia,
>Of course this is true.
>Although, wouldn't you agree that taking enough noise margin into account
>(say 300mV) would cover most SSN in a properly designed PDS? (At least as
>long as the FPGA doesn't bounce too much internally, one has to rely on the
>compiler feedback for that information.) Sure, it (SSN) affects timing, but
>if all else is fine, I believe the impact is acceptable.
>
>Anders,
>how many bits if I might ask? 256? 512? This number will probably get you in
>trouble when using the SSTL2C2 on the V2P regarding the SSO number.
>
>If my poor memory serves me well, I think the V2P is quite sensitive to
>over/undershoot on its IO. (Check the datasheet and with your FAE when in
>doubt.)
>I once simulated a design with 5 cm lines, resulting in (for the data-lines)
>just resistors at the DDR (just like Ravinder) BUT with DCI on the V2P IO
>pads (mind chip dissipation though); guess this won't cut your problem
>though.
>
>As Julia and others have stated, I also prefer proper termination on DDR
>interfaces; it is what the original SSTL2 spec stands for.
>
>Kind Regards,
>Kristiaan
>
>
>-----Original Message-----
>From: Julia Nekrylova [mailto:JNEKRYLO@xxxxxxxxxx]
>Sent: 4-feb-05 21:34
>To: kristiaan.depaepe@xxxxxxxxx; af@xxxxxx; si-list@xxxxxxxxxxxxx
>Subject: RE: [SI-LIST] Re: DDR-1 termination (short point-to-point)
>
>A simple SI and timing simulation would not include SSN effects (ground
>bounce, power noise) that in the presence of terminations are far more
>manageable. This is just a reminder that SSN can kill DDR performance,
>not just reflections and crosstalk.
>
>Regards,
>Julia
>
>
>
>
>------------------------------------------------------------------
>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
>

The weirsp@xxxxxxxxxx e-mail address will terminate March 31, 2005.
Please update your address book with weirsi@xxxxxxxxxx


------------------------------------------------------------------
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: