Problem with AD9283 ADC Expansion module

Dear all,

I have a Mimas V2 Spartan 6 FPGA board with the AD9283 ADC Expansion module. It seems that I can read data from the ADC, but with the two inputs shorted, I read a value of roughly 7 from the adc, and according to the data sheet of AD9283 that corresponds to -480 mV or so. If I apply the a voltage across the two inputs I instead read 16-17 from the ADC, independent of the value and sign of the applied voltage.

Could there be something faulty with the board, or am I doing something wrong?

This is my simple code to read it out:

Code:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity top_adc is
    Port ( Clk12MHz : in  STD_LOGIC;
           adc_data : in  STD_LOGIC_VECTOR (7 downto 0);
           adc_enable : out  STD_LOGIC;
              adc_pwrdown : out STD_LOGIC;
              LED : out STD_LOGIC_VECTOR (7 downto 0);
              reset : in std_logic);
end top_adc;



architecture Behavioral of top_adc is


component divider is
Generic (FACTOR : integer);
Port (clk_12MHz : in  STD_LOGIC;
      clk_out : out  STD_LOGIC;
      reset : in  STD_LOGIC);
end component;


signal tmp : unsigned(7 downto 0) := (others => '0');
signal Clk2Hz : std_logic := '0';

begin
divider_inst: divider generic map(12e6/2) PORT MAP(Clk12MHz,Clk2Hz,Reset);

-- Route the clock to the ADC
adc_enable <= Clk12MHz;

-- Don't power down
adc_pwrdown <= '0';

-- Register the incoming data right away
tmp <= unsigned(adc_data);


process(Clk2Hz)
begin
    if rising_edge(Clk2Hz) then
        LED <= std_logic_vector(tmp);
    end if;
end process;


end Behavioral;

Best regards,
Andreas