Spartan e3 Analog 2 Digital

[StevenNess]

Hi,

i've a problem concerning analog to digital conversion using my spartan e3 fpga.

I set the PreAmp as recommended in the User Guide and want to start analog to digital conversion.

I also disable the other SPI devices in order to read out the MISO properly. But when i've no signal neither on

ADC A nor on ADC B i can read out values, which a different from zero. And the most confusing thing is, that

the values are changing with the time.

I also use a 34 cycles to read out the data properly.

Best regards,

Steve Ness

[ralfn]

Hi Steve,

an analog-digital converter needs a input source with a well-defined impedance.

If you have an open analog input (floating) the ADC provides you with any value. Mostly this value changes slowly.

More details you can take from the following documents:

Troubleshooting Unexpected Voltages, Floating, or Crosstalk on Analog Input Channels

http://digital.ni.com/public.nsf/allkb/B9BCDFD960C06B9186256A37007490CD

You can test the analog input with a battery.

I hope this helps.

With best regards,

Ralf N.

[ralfn]

BTW:

A ready to run example for analog input is included in Exercise 4.1 (see Solutions folder).

LabVIEW FPGA Module Training for Xilinx Spartan 3E XUP Hardware
http://zone.ni.com/devzone/cda/tut/p/id/6848

[StevenNess]

Thank you for your help. In fact is my analog input floating.

I'll tell you what the problem was.