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Is it possible to use the VGA output and XADC at the same time?


I am attempting to sample values from the XADC and use those values to control a video display connected via VGA.  Both of these parts work separately, but when I attempt to combine the hardware for the two, the XADC stops working.  Specifically, the XADC still returns values, and those values still fluctuate slightly, but they don't represent the voltage anymore.

I'm using the XADC in single channel mode, and have tried both channels 6 and 14.  I've connected my analog input to PMOD-JA in the appropriate places for channel 6 and 14.  Both of these channels function perfectly in my XADC only design, but when I add the VGA display hardware they stop working.

The values returned by the XADC still fluctuate, so it's sampling something, just not the thing I want it to sample.  For example, I had a voltage difference of approximately 0.37 volts across channel 14 and some of the 16-bit values returned by the XADC were 206, 187, 196, 226, 201, 220, 201, 187, 222, 229, 192, 213, and 225.  These values stay in this 100-200 range even if the voltage is changed.  Again, the correct values are returned when using the hardware without the VGA display.  Adding the VGA hardware breaks it.

I'm interested to know if anyone has successfully used both the VGA output and the XADC in the same project, and if they had to do anything special to get the setup working.  If necessary, I could provide code or a Vivado project that demonstrates my issue.


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Hi gfrung4,

What board are you using i.e. Basys 3 or Zybo or...? What version of Vivado? Could you attach the project and a screen shot of any warnings?



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