[SI-LIST] AW: Re: DDR-II: SSTL_18 & ODT

Hi D.C.,=20

I do not really aggree with the comment that=20
"ODT is still somewhat controversial, which is why there are provisions =
to disable it altogether."

There are situations, where you will use ODT to ensure SI (e. g. =
Desktop PC system with 2 or 3 Slots @533 ot 666 Mb/s),=20
and there will be implementations, where it may be not necessary to use =
ODT (e. g. P2P systems).
And for this case it is possible to switch off ODT, to save the Power.
And this was the reason to have a "off" setting for ODT too.

JEDEC is not defining how you have to implement a system, it is only =
defining the features, and giving
a possible way to do the job. So, it is totally up to you, how you get =
the system running with the
available features.

regards

Hermann


-----Urspr=FCngliche Nachricht-----
Von: D. C. Sessions [mailto:dcs@xxxxxxxxxxxxxxxx]
Gesendet am: Montag, 19. August 2002 18:31
An: bstott@xxxxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Re: DDR-II: SSTL_18 & ODT


On Mon, 2002-08-12 at 11:35, Bret Stott wrote:

> I am a new member of this list and I have a few questions about =
DDR-II that I=20
> was hoping someone could help me out with.  Currently, I don't have =
access to=20
> JEDEC so most of my information is from alternate sources such as the =
Samsung=20
> DDR-II spec.
>=20
> o Can anyone point me at a SSTL_18 specification?

Yes, but then I'd have to kill you.

Seriously, this should be hitting publication Very Soon Now.
We just recently gave the JEDEC office the go-ahead.  Look
for JESD8-15.

> o Can someone help me understand the on-die-termination strategy for =
DDR-II? =20
> Why are the values 75 & 150 Ohms?  What electrical topology is being =
assumed?

Your basic DDR DRAM topology, w/o the motherboard shunt resistors.
ODT is still somewhat controversial, which is why there are
provisions to disable it altogether.

> o My initial analysis suggests that it is possible to use class I =
drivers for=20
> the address bus (5 load) and also for a point-to-point data bus.  The =
data bus=20
> may require some non-standard termination values though.  Does anyone =
have any=20
> information that supports of refutes this?

There Is No Class One.  SSTL-18 ditches the "Class I" driver
spec since the SSTL-2 class I spec has caused a lot of
confusion and we couldn't find any valid uses for it.

(Yeah, I know that that last if flame bait.  If you don't like
the JC-16 tendency to concentrate on DRAM to the exclusion of
other applications, JOIN THE FREAKING COMMITTEE!)

--=20
| May I have the serenity to accept the things I cannot change, |
|  the strength to change the things I cannot accept, and the   |
|    cunning to hide the bodies of those who got in my way.     |
+------------- D. C. Sessions <dcs@xxxxxxxxxxxxxxxx> -----------+


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