In response to both of these follow up questions regarding accounting = for pcb skew in DDR2 designs (see Jeffery's also): I must confess to = being a DDR SDRAM designer who has tracked with interest the differences = and improvements in DDR2 (but no DDR2 designs....yet), so I will look = for someone more qualified to answer these good questions. Jim=20 Honeywell=20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] = On Behalf Of dayedit@xxxxxxx Sent: Wednesday, April 19, 2006 11:14 PM Subject: [SI-LIST] Re: About the DDR2 Data Tim ing Budget Calculation HI Jim, Also I have the similar problem with Jeffrey in calculating DDR2 timing, = and most time, when considering crosstalk and ISI effects, I get a = negative timing margin. So I wonder whether I double calculating some = effects.We can use derating table to calculate setup/hold time when = differential DQS crossing point Vref(dc) is defined zero, we = needn=A1=AFt consider skew caused by Vil and Vih because setup/hold time = definitions include this effects, but when differential DQS crossing = point isn=A1=AFt zero, according to JEDEC 792B, VIX (ac) ac differential = cross point voltage can be between 0.5 * VDDQ - 0.175V to 0.5 * VDDQ + = 0.175V, it seems that derating table didn=A1=AFt include this effects, = it just reference Vref as a constant, so skew caused by Vref still is = not considered, especially for single ended DQS( here I regard Vref as = variable between Vil and Vih). To get a positive margin, I hope I=A1=AFm = wrong in understanding the parameters.B.R.Greg ------------------------------------------------------------------ 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: =20 //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 =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 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