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Visitor
Visitor
1,549 Views
Registered: ‎02-17-2009

is there a way to read DCI resistor value?

I have an input diff pair configured as DIFF_SSTL12_DCI on a VU13P device.  The POS side is centered around 0.52V and the NEG side is centered around 0.69V.  They should both be centered at 0.6V.  Is there a way to see what the DCI circuitry thinks the resistor value should be?  Is there a way to check if the 2R pullup and 2R pulldown are the same or not (see ug571 v1.7 figure 1-68).

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Moderator
Moderator
1,472 Views
Registered: ‎04-18-2011

There is no way for the customer to read back the setting.
You should think about dropping the DCIReset primitive into the design.
It has a locked status signal and also you can use the reset to redo the calibration. Try that and see if this is just an issue at start-up
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Visitor
Visitor
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Registered: ‎02-17-2009

We already tried DCIReset, it didn't change the behavior.  We weren't sure if we put it in the right place; the documentation is unclear about how many DCIResets there are and where they need to be.  Is there one per SLR?  Or one per I/O bank?

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Moderator
Moderator
1,430 Views
Registered: ‎04-18-2011

Ok,
Did you try slowing down the input if possible?
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Visitor
Visitor
1,424 Views
Registered: ‎02-17-2009

The incorrect voltage bias is present when the driving device is tristated, which is as slow as possible.

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Moderator
Moderator
1,391 Views
Registered: ‎04-18-2011

Can we see a scope shot of both the driving and tri stated cases?

 

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