Hi, two comments: Up to now there is no final SSTL18, but there will be a SSTL18 = eventually! And it is correct, that the ODT values are some compromise between = Power and SI. But there are some more thoughts. First the problem is, that (usually) read data sees different topology = then write=20 data (expect e. g. a star bus topology). So optimization for read is = very often=20 worse for write.=20 In cas of ODT and DDRII the topology for a two slot system is some kind = of asymetric T bus. E. g. the LeadIn on Mobo is 40 Ohm and on the DIMM you do have a = 20 Ohm Stub resistor in series with a 55 Ohm trace. For the Write in a two slot = system, the data sees a 40 Ohm trace, and then 20 + 55 ohm in parallel with the second slot = (20 + 55 ohm).=20 If you are calculating this one, the branch is not to bad matched.=20 And for the 20 + 55 Ohm the 75 Ohm is not the worst termination for the = second slot. In case of a single Slot system the termination of DDRII is done on the = same slot, that is=20 written to (of course, as there is only one slot poplated). To burn not = to much power, the termination is only half of the 2 Slot system. This can be done, as for = a single slot population the SI is not as bad as for the dual slot system. So this is one of the tradeoffs between SI and Power, that Gregory = mentioned=20 regards Hermann -----Urspr=FCngliche Nachricht----- Von: pgregory [mailto:pgregory@xxxxxxxxxx] Gesendet am: Dienstag, 13. August 2002 23:38 An: 'si-list@xxxxxxxxxxxxx' Betreff: [SI-LIST] Re: DDR-II: SSTL_18 & ODT JEDEC has two SSTL specs: SSTL_2 (2.5V) [JESD8-9B] and SSTL_3 (3.3V). There is no SSTL_1 or SSTL_18 JEDEC spec. =20 The HSTL spec is a 1.5V spec [JESD8-6]. The industry has created a=20 defacto standard for HSTL operating at 1.8V (see Micron RLDRAM and=20 QDRII data sheets=20 http://download.micron.com/pdf/datasheets/sram/MT54W1MH18B_4.pdf ) On-die-termination has to balance many things including power and SI. The non-ideal termination is a compromise. See=20 http://download.micron.com/pdf/technotes/TN4606.pdf for a look=20 at some comparison values. -----Original Message----- From: Bret Stott [mailto:bstott@xxxxxxxxxxxxxxxx] Sent: Monday, August 12, 2002 12:35 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] DDR-II: SSTL_18 & ODT Hi SI-gurus, I am a new member of this list and I have a few questions about DDR-II = that I=20 was hoping someone could help me out with. Currently, I don't have = access to=20 JEDEC so most of my information is from alternate sources such as the Samsung=20 DDR-II spec. o Can anyone point me at a SSTL_18 specification? o Can someone help me understand the on-die-termination strategy for = DDR-II? Why are the values 75 & 150 Ohms? What electrical topology is being assumed? o My initial analysis suggests that it is possible to use class I = drivers for=20 the address bus (5 load) and also for a point-to-point data bus. The = data bus=20 may require some non-standard termination values though. Does anyone = have any=20 information that supports of refutes this? Thanks in advance, -Bret ------------------------------------------------------------------ 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 archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 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: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field 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