[SI-LIST] Re: AW: DDR Eye diagrams
- From: john <johndp@xxxxxxxx>
- To: hermann.ruckerbauer@xxxxxxxxxxxx
- Date: Wed, 28 Jul 2004 09:09:46 +0100
David
As well as the level difference mentioned by Hermann, you can also use
the write pre-amble time as a qualifier for the trigger, depending on
the type of scope you are using. Depending on what you are actually
trying to measure I would suggest using the math and statistical
functions of your scope.
Regards
John
hermann.ruckerbauer@xxxxxxxxxxxx wrote:
>Hi David,
>
>there are two methods I usually use (but I not really like both of them)
>
>Usually Write and Reads are different in high and low levels. So do an =
>A-B event trigger, e.g. you want to take a Write (measured at the DRAM), =
>connect a probe to another DQ channel at the controller and set the =
>level so high only a Write is catched. now you should have another probe =
>on the DQS at the DRAM to have a B event, and you can create an eye =
>timing referenced to the DQS for Writes at the DRAM (of course including =
>trigger jitter of the scope).
>If you use the clock as B event you should capture DQ and DQS for the =
>dataeye. Therefore you are missing the bit by bit correlation DQ to DQS =
>(assuming you are using a RT scope), but without this correlation you =
>might see the worst case that can happen over a long period of time more =
>likely!
>
>Another way is to check the WE and RAS signal, and do some kind of logic =
>triggering.
>
>regards
>
>Hermann
>
>-----Urspr=FCngliche Nachricht-----
>Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>Im Auftrag von Novak David
>Gesendet: Mittwoch, 28. Juli 2004 05:19
>An: si-list
>Betreff: [SI-LIST] DDR Eye diagrams
>
>
>For measuring DDR eye diagrams, the best location to measure reads is at =
>=3D the memory controller and the best place to measure writes is at the =
>=3D DDR. For example, measuring reads at the DDR will show more =
>reflections =3D than actually seen by the memory controller (I should =
>mention that I =3D have only series termination).
>
>This sounds simple, but I cannot think of a way to make the scope =3D =
>differentiate between reads and writes. You might suggest that I create =
>=3D a memory test which only does reads or only does writes. However, my =
>=3D worst case signals are when the entire system is running.
>
>Can anyone tell me how to make the scope trigger only on reads or only =
>=3D on writes?
>
>Thanks,
>David
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