Hi Ched, For the SDRAM timing you have to guarantee that both the setup time and the hold time are respected. For the setup time there is this equation: (1) ClockCycleTime = SetupTime + ClockToOutput + ClockSkew + ClockJitter + TimeOfFlight where * SetupTime is the setup time the receiver, either the sdram either the mP,as example * ClockToOutput is the maximum time between the clock edge to a valid signal on the driver * ClockSkew is the total skew between clock driver plus different traces length * ClockJitter is the maximum jiitter of clock * TimeOfFlight is the maximum delay of PCB trace From this equation you can obtain the maximum trace length. This equation means you have a defined (stable) signal a SetupTime before the receiver reads the value. You have to guarantee the signal comes a SetupTime before isread. For the hold time the equation is: (2) ClockToOutput + TimeOfFlight = HoldTime + ClockSkew + ClockJitter where * ClockSkew and ClockJitter are the same of equation (1) * ClockToOutput is the minimum time between the clock edge to a valid signal on the driver * TimeOfFlight is the minimum delay of PCB trace From this equation you can obtain the minimum trace length. This equation means that the receiver needs a stable signal during the sampling. ou have toguarantee the signal is not de-asserted before the receiver read it. Hope this helps Carlo Ched-Chang Chai wrote: Dear all, I have a question about SDRAM timing. I came across the following equation from an application note: a= clock cycle time - access time - jitter - timeofflight (PCB trace) -InputSetup - InputHold If a is positive, the maximum clock frequency that the SDRAM can operate = 1/clock cycle time. Is this calculation correct? Otherwise, please advise me how to calculate the maximum trace length limit from the access time, setup/hold times, etc? Thank you very much in advance. -- Regards, Chai _________________________________________________________________ Are you in love? Find a date on MSN Personals http://match.msn.com.my/[1] ------------------------------------------------------------------ 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[2] For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http:/www.si-list.org[3] List archives are viewable at: //www.freelists.org/archives/si-list[4] or at our remote archives: http://groups.yahoo.com/group/si-list/messages[5] Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu[6] -- Carlo Bleu ITALTEL s.p.a. - Product and Technologies Technology &Product Development - Hardware Platform tel. 02 4388 9056 e-mail: carlo_franco.bleu@xxxxxxxxxx 20019 - via Reiss Romoli Castelletto Settimo Milanese (MI) - ITALY --- Links --- 1 http://match.msn.com.my/ 2 //www.freelists.org/webpage/si-list 3 http:/www.si-list.org 4 //www.freelists.org/archives/si-list 5 http://groups.yahoo.com/group/si-list/messages 6 http://www.qsl.net/wb6tpu ------------------------------------------------------------------ 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.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