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YellowYoung

Pmod ADC and FMC pins

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Hi there, 

I used to use pmod adc at the pmod connector on zedboard, recently I turned to use the FMC connections so that more IOs could be used. Following this, I specified some pins on the FMC and connected them to the pmod adc card, however, the adc does not work. 

Is there ant difference between the pins on the pmod and on the FMC connector (LPC pins)?

Thank you so much!

image.png.ef11ad5ac464df09154cfe45d97403e2.png

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Hi @YellowYoung,

Which FMC card and which particular Pmod ADC are you using? I know that the FMC pins are set to certain voltages (as per section 2.9.1 in the Zedboard Hardware User Guide from Avnet) and by default are set to 1.8V and can be adjusted to operated at 2.5V instead via J18.

The Pmod AD1 (as it looks like you have shown a picture of) operates at 3.3V, which while possible to get on the Zedboard FMC by soldering an external connection, though it does warn that this voltage rail potentially the most damaging and if the wrong voltage is selected to the jumper, the pins on the FMC card or Zedboard can become damaged.

At first glance, my guess would be that the voltages are currently not compatible so the ADC does not respond.

Let me know if you have any questions.

Thanks,
JColvin

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@JColvin

Hi JColvin,

Thank you so much for your response.

The FMC board I'm using is HW-FMC-105-Debug, which helps pull out all the zynq pins. I did notice that in the beginning, if I assign the pins on the FMC board to generate high level, it is measured as 2.5V, then I found there's a Vadj jumper selection on the ZedBoard, and I switched it from 2V5 to 3V3, then the pin voltage on the FMC board becomes 3.3V. I had thought this would help but it seems the pmod still does not work.

Any suggestion?

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Hi @YellowYoung,

I haven't worked with that particular FMC board, but looking at the Xilinx made UG537 for it, I presume you are attempting to connect the Pmod to J16 and have configured the J6 header to provide 3.3V power?

Thanks,
JColvin

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Hi @JColvin

Thanks for your reply!

On the Zedboard, I switched the Jumper on J18 from 2V5 to 3V3. But on the FMC board, I didn't do anything on J16. Do you mean that I shall do some pin configuration on the FMC board too? Is the VADJ mensioned in UG537 the same to the Vadj on the zedboard?

Thank you!

image.png.eeacbd730f7a887fa8a9f81cb4dd45aa.pngimage.thumb.png.a224ced66ddf346a0025cf7838585166.png

 

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Hi @YellowYoung,

Truthfully, I don't know if this is the case; J16 just happened to look the most convenient with regards to physical connectivity to the Pmod. If you are instead using external wiring and routing your specific pins as well as an exposed VADJ pin that is providing 3.3V to the power pin of the Pmod, then in theory that would be electrically compatible. The user guide also shows that the VADJ "power good" LEDs also work with 3.3V, so I do not think there is anything physically preventing this, though I have not tested this for myself as I have not used the board.

I presume that in your .xdc file, you updated the IO voltage standard that you are using?

Thanks,
JColvin

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Hi @JColvin

Yes, in the design constraints, all the IO standard are specified as 3.3V. I've tried to follow the J16 and J6 header configuration but still didn't make it work.

image.png.cebba7acad1747ef5adab82089f34411.png

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Hi @YellowYoung,

I apologize for the long delay. I'm not certain what else would have to be done differently. Since you have set the IOStandard and worked with the header changes, what I would attempt to do is to use a logic analyzer or multimeter to confirm that signals are successfully being transmitted from the FPGA through the FMC to the FMC card. If they are not being transmitted, then I would be concerned if the Bank the FMC pins are located on are damaged.

Thanks,
JColvin

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