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-- VHDL CODE by Gerry O'Brien - HD44780 LCD Controller STATE_MACHINE

--==================================================--

--

-- VHDL Architecture DE2_LCD_lib.TOP_LCD_DE2.LCD_DISPLAY_arch

--

-- Created:

--          by - Gerry O'Brien 

--          WWW.DIGITAL-CIRCUITRY.COM

--          at - 15:30:18 26/03/2015

-- 

-- using Mentor Graphics HDL Designer(TM) 2010.3 (Build 21)

--

LIBRARY IEEE;

USE  IEEE.STD_LOGIC_1164.all;

USE  IEEE.STD_LOGIC_ARITH.all;

USE  IEEE.STD_LOGIC_UNSIGNED.all;

ENTITY LCD IS

   PORT(

                reset             : IN     std_logic;  -- Map this Port to a Switch within your [Port Declarations / Pin Planer]  

                CLOCK_50          : IN     std_logic;  -- Using the DE2 50Mhz Clk, in order to Genreate the 400Hz signal... clk_count_400hz reset count value must be set to:  <= x"0F424"

                LCD_RS            : OUT    std_logic;

                LCD_EN            : OUT    std_logic;

                LCD_RW            : OUT    std_logic;

                LCD_ON            : OUT    std_logic;

                LCD_BLON          : OUT    std_logic;

                LCD_DATA          : INOUT       STD_LOGIC_VECTOR(7 DOWNTO 0);

                lcd_on_sig                : IN          STD_LOGIC;

                next_char                 : IN          STD_LOGIC_VECTOR(7 DOWNTO 0);

                char_count        : OUT         STD_LOGIC_VECTOR(4 downto 0);

                clk400hz              : OUT             STD_LOGIC

   );

END LCD ;

--

ARCHITECTURE RTL OF LCD IS

  type state_type is (hold, func_set, display_on, mode_set, print_string,

                      line2, return_home, drop_LCD_EN, reset1, reset2,

                       reset3, display_off, display_clear);

  signal state, next_command         : state_type;

  signal data_bus_value                          : STD_LOGIC_VECTOR(7 downto 0);

  signal clk_count_400hz             : STD_LOGIC_VECTOR(19 downto 0);

  signal char_count_sig              : STD_LOGIC_VECTOR(4 downto 0);

  signal clk_400hz_enable,LCD_RW_int : std_logic;

  signal data_bus                    : STD_LOGIC_VECTOR(7 downto 0);

  signal LCD_CHAR_ARRAY              : STD_LOGIC_VECTOR(3 DOWNTO 0);

BEGIN

LCD_DATA        <= data_bus;

data_bus        <= data_bus_value when LCD_RW_int = '0' else "ZZZZZZZZ";

LCD_RW          <= LCD_RW_int;

char_count      <= char_count_sig;

clk400hz                <= clk_400hz_enable;

--======================= CLOCK SIGNALS ============================--  

process(CLOCK_50)

begin

      if (rising_edge(CLOCK_50)) then

         if (reset = '0') then

            clk_count_400hz <= x"00000";

            clk_400hz_enable <= '0';

         else

            if (clk_count_400hz <= x"0F424") then          -- If using the DE2 50Mhz Clock,  use clk_count_400hz <= x"0F424"  (50Mhz/400hz = 12500 converted to HEX = 0F424 )   

                   clk_count_400hz <= clk_count_400hz + 1; --  In Theory for a 27Mhz Clock,  use clk_count_400hz <= x"01A5E"  (27Mhz/400hz = 6750  converted to HEX = 01A5E )                                       

                   clk_400hz_enable <= '0';                --  In Theory for a 25Mhz Clock.  use clk_count_400hz <= x"0186A"  (25Mhz/400hz = 6250  converted to HEX = 0186A )

            else

                   clk_count_400hz <= x"00000";

                   clk_400hz_enable <= '1';

            end if;

         end if;

      end if;

end process;

--==================================================================--    

--======================== LCD DRIVER CORE ==============================--   

--                     STATE MACHINE WITH RESET                          -- 

--===================================================-----===============--  

process (CLOCK_50, reset)

begin

        if reset = '0' then

           state <= reset1;

           data_bus_value <= x"38"; -- RESET

           next_command <= reset2;

           LCD_EN <= '1';

           LCD_RS <= '0';

           LCD_RW_int <= '0';

        elsif rising_edge(CLOCK_50) then

             if clk_400hz_enable = '1' then

              --========================================================--                 

              -- State Machine to send commands and data to LCD DISPLAY

              --========================================================--

                 case state is

                 -- Set Function to 8-bit transfer and 2 line display with 5x8 Font size

                 -- see Hitachi HD44780 family data sheet for LCD command and timing details

--======================= INITIALIZATION START ============================--

                       when reset1 =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"38"; -- EXTERNAL RESET

                            state <= drop_LCD_EN;

                            next_command <= reset2;

                            char_count_sig <= "00000";

                       when reset2 =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"38"; -- EXTERNAL RESET

                            state <= drop_LCD_EN;

                            next_command <= reset3;

                       when reset3 =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"38"; -- EXTERNAL RESET

                            state <= drop_LCD_EN;

                            next_command <= func_set;

                       -- Function Set

                       --==============--

                       when func_set =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"38";  -- Set Function to 8-bit transfer, 2 line display and a 5x8 Font size

                            state <= drop_LCD_EN;

                            next_command <= display_off;

                       -- Turn off Display

                       --==============-- 

                       when display_off =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"08"; -- Turns OFF the Display, Cursor OFF and Blinking Cursor Position OFF.......(0F = Display ON and Cursor ON, Blinking cursor position ON)

                            state <= drop_LCD_EN;

                            next_command <= display_clear;

                       -- Clear Display 

                       --==============--

                       when display_clear =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"01"; -- Clears the Display    

                            state <= drop_LCD_EN;

                            next_command <= display_on;

                       -- Turn on Display and Turn off cursor

                       --===================================--

                       when display_on =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"0C"; -- Turns on the Display (0E = Display ON, Cursor ON and Blinking cursor OFF) 

                            state <= drop_LCD_EN;

                            next_command <= mode_set;

                       -- Set write mode to auto increment address and move cursor to the right

                       --====================================================================--

                       when mode_set =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"06"; -- Auto increment address and move cursor to the right

                            state <= drop_LCD_EN;

                            next_command <= print_string;

--======================= INITIALIZATION END ============================--                          

--=======================================================================--                           

--               Write ASCII hex character Data to the LCD

--=======================================================================--

                       when print_string =>

                            state <= drop_LCD_EN;

                            LCD_EN <= '1';

                            LCD_RS <= '1';

                            LCD_RW_int <= '0';

                               -- ASCII character to output

                               if (next_char(7 downto 4) /= x"0") then

                                  data_bus_value <= next_char;

                               else

                                    -- Convert 4-bit value to an ASCII hex digit

                                    if next_char(3 downto 0) >9 then

                                    -- ASCII A...F

                                      data_bus_value <= x"4" & (next_char(3 downto 0)-9);

                                    else

                                    -- ASCII 0...9

                                      data_bus_value <= x"3" & next_char(3 downto 0);

                                    end if;

                               end if;

                            state <= drop_LCD_EN;

                            -- Loop to send out 32 characters to LCD Display (16 by 2 lines)

                               if (char_count_sig < 31) AND (next_char /= x"fe") then

                                   char_count_sig <= char_count_sig +1;

                               else

                                   char_count_sig <= "00000";

                               end if;

                            -- Jump to second line?

                               if char_count_sig = 15 then

                                  next_command <= line2;

                            -- Return to first line?

                               elsif (char_count_sig = 31) or (next_char = x"fe") then

                                     next_command <= return_home;

                               else

                                     next_command <= print_string;

                               end if;

                       -- Set write address to line 2 character 1

                       --======================================--

                       when line2 =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"c0";

                            state <= drop_LCD_EN;

                            next_command <= print_string;

                       -- Return write address to first character position on line 1

                       --=========================================================--

                       when return_home =>

                            LCD_EN <= '1';

                            LCD_RS <= '0';

                            LCD_RW_int <= '0';

                            data_bus_value <= x"80";

                            state <= drop_LCD_EN;

                            next_command <= print_string;

                       -- The next states occur at the end of each command or data transfer to the LCD

                       -- Drop LCD E line - falling edge loads inst/data to LCD controller

                       --============================================================================--

                       when drop_LCD_EN =>

                            LCD_EN <= '0';

                            state <= hold;

                       -- Hold LCD inst/data valid after falling edge of E line

                       --====================================================--

                       when hold =>

                            state <= next_command;

                            LCD_BLON <= '1';

                                                                         LCD_ON <= lcd_on_sig;

                       end case;

             end if;-- CLOSING STATEMENT FOR "IF clk_400hz_enable = '1' THEN"

      end if;-- CLOSING STATEMENT FOR "IF reset = '0' THEN" 

end process;

END ARCHITECTURE RTL;