Stepper

About: This code is capable of running a 4 wire 2 phase stepper motor through our custom pcb. All four half bridges are used and must be put in a certain order according to the motor. The enable pins go to the top fets, while the output pins go to the bottom fets. In order to change the frequency of the pwm, change which bits of timer are sampled to get the commutation (lower bits sampled creates higher frequency).

Code:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use ieee.std_logic_unsigned.all;

entity stepper is
   Port ( clk : in STD_LOGIC;
          start : in  STD_LOGIC;
          direction : in  STD_LOGIC;
          speed : in STD_LOGIC_VECTOR(1 downto 0);
          enable : out std_logic_vector(3 downto 0);
          output : out  STD_LOGIC_VECTOR(3 downto 0));
end stepper;

architecture Behavioral of stepper is
signal timer : std_logic_vector(26 downto 0) := (others => '0');-- "0000000000";
signal q, q1, q2, q3, q4 : std_logic_vector(3 downto 0) := "0000";

begin

  enable <= "0000";
  process(clk)
  begin
     if rising_edge(clk) then
        if(start = '0') then
           timer <= (others => '0');--"0000000000";
        elsif(direction = '1') then
           timer <= timer + 1;
        else
           timer <= timer - 1;
        end if;
     end if;
  end process;
  
  with timer(26 downto 25) select q1 <=
     "0001" when "00",
     "0010" when "01",
     "0100" when "10",
     "1000" when others;
     
  with timer(24 downto 23) select q2 <=
     "0001" when "00",
     "0010" when "01",
     "0100" when "10",
     "1000" when others;
  with timer(22 downto 21) select q3 <=
     "0001" when "00",
     "0010" when "01",
     "0100" when "10",
     "1000" when others;
  with timer(20 downto 19) select q4 <=
     "0001" when "00",
     "0010" when "01",
     "0100" when "10",
     "1000" when others;
     
  with speed select q <=
     q4 when "00",
     q3 when "01",
     q2 when "10",
     q1 when others;
      
  with start select output <=
     (   not q) when '1',   -- removed NOT
     "1111" when others;   --changed from "1111"

end Behavioral;