[SI-LIST] Re: DDR-1 termination (short point-to-point)
- From: "Novak David (TTE)" <david.novak@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 4 Feb 2005 15:49:51 -0500
That begs the question, what is different about DDR that allows a 1.5V
shoot spec? Are the protection diodes in these devices somehow different
from typical ICs?
When you say that the diode would be on at 400mV, do you mean that it
would begin turning on at that point?=20
David=20
-----Original Message-----
From: Dennis Han [mailto:Dennis.Han@xxxxxxxxxxx]=20
Sent: Friday, February 04, 2005 3:42 PM
To: Novak David (TTE); si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: DDR-1 termination (short point-to-point)
How much overshoot an IC can handle is usually a function of the
protection diodes in the IC. Turning these on constantly adds power to
the IC and it adds transients to the IC's power and ground planes. It
is best to keep the diodes off. That is probably why the spec is 300
mV. 400 mV would have the diode turned on.
Dennis
----- Original Message -----
From: "Novak David (TTE)" <david.novak@xxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Friday, February 04, 2005 12:45 PM
Subject: [SI-LIST] Re: DDR-1 termination (short point-to-point)
> Yes, but most memory controllers spec. a 300mV(max) for 'shoots.
>
> The interesting question here is how real is that 300mV spec? If the
DDR
> can handle more, why can't the memory controller?
>
> David=3D20
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Landrum, Chris
> Sent: Friday, February 04, 2005 12:03 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: DDR-1 termination (short point-to-point)
>
> Doesn't DDR1 allow for overshoot/undershoot up to 1.5V as long as it
is
> for a short period of time (500pS or so)?=3D3D20
>
> -Chris
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Novak David (TTE)
> Sent: Friday, February 04, 2005 10:18 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: DDR-1 termination (short point-to-point)
>
> The DDR will never be a "slow drive". However, the x32 GDDR parts do
> allow more control over drive strength.
>
> As long as you keep the lines short, you should have no problems with
a
> simple series resistor in each line. This is a very common termination
> scheme for point-to-point DDR designs.
>
> If it were not for the 300mV overshoot specs. on most DDR memory
> controllers, you wouldn't even need the series resistors.
>
> David
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Anders Frederiksen
> Sent: Thursday, February 03, 2005 5:00 PM
> 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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>=20
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