process (clk)
if falling_edge(clk) then
adc <= '1';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '1';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '0';wait for 40ns;
adc <= '1';wait for 40ns;
end if;