how to decide read time from SDRAM via SDRAM controller

process (iCLK,iRESET_n)

begin

if iRESET_n='0' then

az_addr_to_sdr <=std_logic_vector'("10000000000000000000000000");

az_rd_n_to_sdr <= '1';

az_wr_n_to_sdr <= '0';

elsif iCLK'event and iCLK = '1' then

if state='1' then

az_addr_to_sdr <=std_logic_vector'("10000000000000000000000000")+count;

az_rd_n_to_sdr <= '1';

az_wr_n_to_sdr <= '0';

az_cs_to_sdr <='1';

tDATA_to_sdr <=(DATA_for_test&std_logic_vector'("11111111111111111111111111111111111111111111111111111111"));

oDATA <= "00001111";

-- when state='1' write data to SDRAM

else

az_addr_to_sdr <=std_logic_vector'("10000000000000000000000000")+count-std_logic_vector'("01000000000000000000000000");

az_rd_n_to_sdr <= '0';

az_wr_n_to_sdr <= '1';

az_cs_to_sdr <='1';

oDATA <= data_from_dq(7 downto 0);

-- when state='0' read data from SDRAM

end if;

end if;

end process;

process (iCLK, iRESET_n)

begin

if iRESET_n='0' then

count <= std_logic_vector'("00000000000000000000000000");

elsif iCLK'event and iCLK='1' then

count <= count + std_logic_vector'("00000000000000000000000001");

if count >= std_logic_vector'("01000000000000000000000000") then

state <= '0';

else

state <= '1';

end if;

end if;

end process;

That is the whole program I have used. The problem is that i can't read data from SDRAM.

Output data is supposed to be "11111111" but the vale displayed are always "00000000". I don't know if I haven't written.