Andy has a very good point. Many source-synchronous devices fire clock (usually called the strobe output) and the data bits at the same time, and rely on the PCB to supply the proper offset between signals for the receiver. I've usually seen the words "edge aligned" to describe the strobe-data relationship for these parts. In such a case, it would be common to see the data INvalid window spec'd with respect to the stobe. I believe Andy is correct, and that is what's going on here. Todd. Todd Westerhoff Signal Integrity Engineer Cisco Systems 250 Apollo Drive - Chelmsford, MA - 01824 email:twesterh@xxxxxxxxx ph: 978-497-0272 ============================================ "When did the choices get so hard, with so much more at stake? Life gets mighty precious when there's less of it to waste" - Bonnie Raitt, "Nick of Time" -- Binary/unsupported file stripped by Ecartis -- -- Type: application/ms-tnef -- File: winmail.dat ------------------------------------------------------------------ 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