Why does a sdram interface drive the data to only 2.0V?

[kinysh]

sdram interface

Hi:

I have a sdram interface.
The sdram chip only drive the data to about 2.0v as high.
how could this happen.
the sdram controller chip can drive the data onto 2.8v.

How could this happen, however all the timing is correct.
can anyone help me?

 

[ted]

It would be substantially easier to try to help you if you would tell exactly which chips you use and which power supply voltages are present.

The more details you give for your particular design (even a fragment of the schematics might help), the more easier it is to understand the issue!

Ted

 

[kinysh]

Hi:

Thanks a lot.
I finally find the problem.

We use a seperate power supply for sdram, and the sdram is not even powered on.
Seems there is some coupling power from other pin make the sdram work.

I have never met this before.

Bests
kinysh