Itzhak Hirshtal Wrote: The answer to your question depends on the chip vendor's definition! I'm accustomed to a definition which is in respect to the strobe <<output>> pin, but Mr. Riazi's definition for a source-synchronous design seems to be in respect to the strobe <<input>> pin, that's why he has both Tco_data and Tco_strobe (see his answers to me). I also understand that he refers to a design in which the strobe signal is used to capture the data on the <<opposite edge>> than the edge on which the data is transmitted. <<I>> refered to a source-synchronous bus which samples the data at the receiver on the same dege as the one used to transmit the data. Hi Itzhak: Please clarify: "he refers to a design in which the strobe signal is used to capture the data on the <<opposite edge>> than the edge on which the data is transmitted. <<I>> refered to a source-synchronous bus which samples the data at the receiver on the same dege as the one used to transmit the data" The Source synchronous computer front-side bus (FSB / GTL) designs I have simulated, have included a chipset (example: CMIC-LE ) plus two or more processors (example: Pentium IV). These buses have operated at 133 or 100 MHz. When the chipset drives, it first transmits data signals and a short while later the associated strobes. To ensure proper functioning of such source synchronous buses, the strobe must be timely transmitted to satisfy the setup and hold requirements of the receiver latch. The ideal offset between data and strobe is usually 90 degrees assuming 50% duty cycle. All agents on FSB data interface are bi-directional; therefore, a complete GTL simulation necessitates not only considering the case of chipset driving but also when a Middle or the End processor drives. Common clock timing analysis is required because of data to bus clock relationships; whereas, the data to strobe relation dictates source synchronous setup and hold margin computations. When generating/interpreting a source synchronous timing spreadsheets, it is important to take into account that a group of data signals (for example 16 data bits) can share the same strobes. Thank you, Abe Riazi ServerWorks ------------------------------------------------------------------ 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