[SI-LIST] Re: SDRAM Timing
- From: Bleu Carlo <Carlo_franco.Bleu@xxxxxxxxxx>
- To: ched_chang@xxxxxxxxxxx
- Date: Thu, 20 Nov 2003 19:08:33 +0100
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
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-- 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
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