Question

1. Design a blinking LED with two speeds - slow and fast.

Specification

To change from slow to fast press Button 1 and fast to slow press Button 2.

Reset puts the machine to slow blinking.

entity blink is port (b1, b2, ck, reset: in std_logic;

z: out std_logic);

end blink;

Answer 1

library IEEE;  
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity blink is

    port (b1, b2, ck, reset: in std_logic;

z: out std_logic);

end blink;

architecture behavioural of blink is

signal counter : std_logic_vector(3 downto 0);

begin

     process (clk)

     begin

        if (clk'even and clk = '1') then

         if (rst = '1') then

            counter <= "0000";

         else

         if(b1 = '1') then

          if (counter = "0111") then

                 counter <= "0000";

              end if;

            elsif (b2 = '1') then

               if (counter = "1111") then

                  counter <= "0000";

                end if;

            end if;

   counter <= counter + 1;

      end if;

   end if;

   end process;

   process (b1, b2, rst, counter)

   begin

     if (rst = '1') then

        blink <= '0';

    else

        if(b1 = '1') then

            if (counter = "0111") then

                blink <= not blink;

            end if;

       else   -- with reset or with b2

            if (counter = "1111") then

                blink <= not blink;

            end if;

       end if;

     end if;

end process;

end behavioural;