Hi Kathir, Last week we've talked a similar topic named" DDR2 design issues?" ,Maybe look more details about this Pull-up terminal resistor Rtt will help you.The JEDEC's SSTL interface standard is orginaly from the computer industry.At the PC motherboard ,you will have 2 or more DIMM memory module,of cause it will have stub .This unbalanced stub will cause reflection and ringing problem at high speed. The SSTL use two method to solve this SI pr oblem,one is Stub Seris Resistor(That's why called SSTL),the other is pull up terminal resistor, Rtt; The Rtt have two functions: 1.Terminal at the end,eliminate the fist reflection,better for overshoot and ringing; 2.More fast risf/fall time, good for high speed response. So it is just for better performance but not neccesary. If your design not use DIMM module or not have such stub problems,not have too many DDR loads and the signal speed is not very high,for example 160MHz,you may operate without requiring Rtt---But do enough simulation before decision. Good luck! LIU Luping Subject: [SI-LIST] Re: DDR1 without VTT termination Date: Tue, 1 Apr 2008 08:50:27 +0530 From: <ravi.potana@xxxxxxxxx> Hello Kathir, Please refer to appnote http://download.micron.com/pdf/technotes/DDR/tn4614.pdf from Micron. This may give you some help. Some system designs can operate without requiring VTT. The approximate system boundaries enabling VTT exclusion are: * Two or fewer DDR components in the system * Moderate current draw * Trace length <2in (5cm) * SI and drive strengths within data sheet limits (determined through simulation) Regards Ravi -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Kathiresan K Sent: Monday, March 31, 2008 7:48 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] DDR1 without VTT termination Hi, I need to have a single chip DDR1 (160 MHz, 16-Bit) memory for a processor. I don't want to provide VTT terminations. I'll keep the trace length as minimum as possible. I may provide series termination but I haven't done pre-layout simulation yet. Can somebody please clarify whether it can be designed without VTT termination? If yes, what can be the maximum trace length I go for? If I'm providing series termination, should I provide at both the ends for bi-directional signals? Regards, Kathir This e-mail and its attachments contain confidential information from HUAWEI, which is intended only for the person or entity whose address is listed above. Any use of the information contained herein in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender by phone or em ail immediately and delete it! ***************************************************************** ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net 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