[SI-LIST] DDR delay & skew
- From: "Ched-Chang Chai" <ched_chang@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 10 Dec 2002 11:09:04 +0800
Dear all,
I am confused about how to measure the DDR-SDRAM delay.
I was told that there are 2 different methods in measuring the delays:
Method 1:
- L->H : from Vref of the driver signal to Vinh of the receiver signal
- H->L : from Vref of the driver signal to Vinl of the receiver signal
Method 2:
- L->H & H->L : from Vtt of the driver signal to Vref of the receiver signal
[Note: L->H means signal transitions from LOW to HIGH and the other way
round for H->L]
Can I know which method is correct or is there any other standard method?
What about the delay for DDR differential clock? I measure delays from the
crossing point of the driver signals to the crossing point of the receiver
signals. Is this correct?
And lastly, how to calculate the skew requirement from the Controller/DDR
data sheets?
Thank you very much in advance.
--
Regards,
Chai
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