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Contributor
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Registered: ‎01-13-2014

Using FMC Debug Card to access XADC auxiliary inputs

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Hello, I am using the VC707 Eval kit with the AMS101 card and the FMC debug card. My goal is to use the XADC to digitize several analog inputs. 

 

I've implemented a microblaze soft processor, and have software running on that which can digitize a single-ended bipolar input on Vp/Vn. Now I'm interested in expanding to other channels, which I found can be accessed using the FMC card. I believe I've tracked down the correct pins, but I can't seem to get any meaningful output when I apply an analog signal. All I've done is go into my software (using xilinx sdk) and change the channel variables from Vp/Vn to the corresponding aux channel. I can see a change when I apply a signal, but it seems to be a periodic voltage spike of a random value. 

 

Are there special conditions to consider when switching from the dedicated analog Vp/Vn to an auxilary channel? Is there any preferred way to use a single-ended signal with a differential input? I think I've tried every configuration imaginable. 

 

Any help is appreciated!

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Contributor
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Registered: ‎01-13-2014

Yes, aparently I had the aux pins set as default on the hardware desing level. The output is as it should be

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Contributor
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Anyone? At this point I have no idea if the issue is the FMC card, improper signal filtering, something wrong with my hardware design or microblaze software... It seems to me it should be straightforward to move a signal from Vp/Vn to an aux channel.
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Xilinx Employee
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Registered: ‎01-03-2008

Did you connect the N-side of the pin to ground?  If not then this is likely the problem.

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Contributor
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Should it be tied to the XADC ground? That is my current setup. 

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Xilinx Employee
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Registered: ‎01-03-2008

That would be hard to do as the XADC ground is under the FPGA and not on the XM105.  I meant connected to ground on the XM105.

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Contributor
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Aren't the grounds on the AMS Card connected to XADC ground? I have N connected there.

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Xilinx Employee
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> Aren't the grounds on the AMS Card connected to XADC ground? I have N connected there.

 

After re-reading your posts I am very confused as to what you are doing and the connections in your system.  Please take a photograph of your system setup, annotate it with descriptions of the connections and post it.

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OK I'll see what I can do. I just have the AMS card and FMC debug card plugged in, I have a wire connecting pin J3 39 on the FMC and AGND on the AMS card. My input high is on J3 38 and input ground is on J3 39 (which again is connected to AMS ground), these pins correspond to Vaux6 on the XADC if I have followed the documentation correctly.

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board setup.jpg

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I'm hoping it's a problem with my constraints, checking now.

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Xilinx Employee
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Registered: ‎01-03-2008

> I have a wire connecting pin J3 39 on the FMC and AGND on the AMS card.

> My input high is on J3 38 and input ground is on J3 39

 

The resolution in the photo and the angle isn't ideal (even after zooming in), but it looks like signal is going to J3.9 which is HA02_P and the GND to J3.10 which is HA12_P.   If this is correct then this is one problem with the setup as the GND should be connected to J3.11 which is HA02_N.

 

> these pins correspond to Vaux6 on the XADC

 

The HA02_P pin is connected to AD7P and HA02_N is connected to AD7N, so this is likely a second problem in your design as this isn't AUX6, but AUX7.   The text in the photo however says AUX7, so I don't know which one you mean. If you want to stay with AUX6 then this is connected to HA09_P/J3.37 and HA09_N/J3.39.

 

Lastly, the GND should be connected directly from the BNC to J3.10 (AD7P/HA02_N) and not connected to the AMS-101 board. 

 

XM105_conn.PNG

 

 

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Contributor
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Registered: ‎01-13-2014

Yes, aparently I had the aux pins set as default on the hardware desing level. The output is as it should be

View solution in original post

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