[SI-LIST] Re: DDR-1 termination (short point-to-point)
- From: "Anders Frederiksen" <af@xxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 4 Feb 2005 18:08:45 +0100 (CET)
> Anders,
Kristian,
> Is this DDR333?
Yes!
> In my experience this requires SSTL2C2 on the V2P for the datalines, strobes
> & clocks; these pins are quite fast (0.7 ns ?), putting you right on the
> edge with 5cm.
Hmm - I was hoping there would be margin for using slower drivers.
> The low impedance of the DDR drivers will probably kill
> (overshoot) your V2Pro if no termination is used.
I'd expect the V2Pro to clamp any "nasty" overshoot. But you might be right :-(
A small dirty series resistance near the DDR might limit this - without trashing
writes...
> You might get away with
> the "reduced drive" of the DDR, if possible.
Got to look into that.
> My bet is to simulate it, if you want to minimize the amount of termination
> required.
I was afraid of that ;-)
I'm all new in simulation (don't even know if I have access to simulation tools
accepting IBIS or whatever's available for DDR and Virtex in/outputs.) and
short on
time - so I'll cut any corner that seems safe!
In any case I'd prefer simulation AND experience - just as long as the latter
does
not come from my own respins *s*...
Cheers (have a great weekend!),
Anders
> Kind Regards,
> Kristiaan
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Anders Frederiksen
> Sent: 3-feb-05 23:00
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] DDR-1 termination (short point-to-point)
>
>
> I'm connecting a lot of DDR1 ram to a FPGA (Virtex2pro). Common
> schemes recommended is "embedding a DIMM design" (which would be
> plain stupid imho) and doing a full parallel termination in both ends
> (typically in 0402). The latter is naturally sensible - but it occurs
> to be kind of a overkill for ponit-to-point lines of "only" 5cm (~2")
> or less. Has anyone experience with simpler termination schemes? I
> mean for standard busses one would rely on slow drivers only...
>
> Cheers,
> Anders
>
>
>
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