Jack Born wrote:
> I would like to connect 3.5 mm audio jack to nexys 3 board
Why? For what reason?

> but have no idea how to do so..
Fist step has absolutely nothing to do with FPGAs or VHDL: you must 
connect an AD converter to the FPGA.

> I am a beginner with regards to fpgas and vhdl coding
Then don't start with such a fairly demanding task (for a beginner). 
Instead start with the "blinking led", the "chasing light", and some 
RS232 and VGA, just to learn the very basics of hardware design. If you 
do not, you will crash...

Jack Born wrote:
> not sure how to connect the audio jack's left and right channels to the
> respective data 1 and data 2 pins.
Not at all. Read the documentation for the ADC module, then you will see 
that you have to connect the audio source to P1 and P3. Data1 and Data2 
are the digital serial ADC outputs.

Jack Born wrote:
> But how can a 3.5 mm jack be connected to 2 ports simultaneously?
It may be a stereo jack...
http://en.wikipedia.org/wiki/Phone_connector_%28audio%29

Jack Born wrote:
> yes but how do i connect the stereo jack with the adc converter shown in
> the picture?
Get a soldering iron and start. Maybe you must add a offset voltage to 
get the audio signal into mid range of the adc input:

1

The AD1 converts an analog input signal ranging from 0-3.3 volts 

2

to a 12-bit digital value in the range 0 to 4095.

So you will need something like this here:

1

                o

2

                |

3

               10k   

4

                |

5

In Left   --||--o---- P1 of ADC

6

         470n   |

7

               10k   

8

                |

9

               GND

10

11

In GND ---.

12

          |

13

         GND

14

15

                o 3V3

16

                |

17

               10k   

18

                |

19

In Right  --||--o---- P3 of ADC

20

         470n   |

21

               10k   

22

                |

23

               GND

> with the adc converter shown in the picture
Its an AD1 module from Digilent. Just WRITE down this little fact 
instead of digging in the mud for over 2 hours just to find out a little 
snippet of information...

Maybe this could be a solution for you (ADC included...):
http://uk.farnell.com/digilent/210-191/peripher-mod-stereo-jack-pmodi2s/dp/2061865