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-- Copyright (c)2013, 2020 Jeremy Seth Henry

-- All rights reserved.

--

-- Redistribution and use in source and binary forms, with or without

-- modification, are permitted provided that the following conditions are met:

--     * Redistributions of source code must retain the above copyright

--       notice, this list of conditions and the following disclaimer.

--     * Redistributions in binary form must reproduce the above copyright

--       notice, this list of conditions and the following disclaimer in the

--       documentation and/or other materials provided with the distribution,

--       where applicable (as part of a user interface, debugging port, etc.)

--

-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``AS IS'' AND ANY

-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

-- DISCLAIMED. IN NO EVENT SHALL JEREMY SETH HENRY BE LIABLE FOR ANY

-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND

-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

--

-- VHDL Entity: o8_hd44780_4b

-- Description: Provides low-level access to a "standard" character LCD using

--               the ST/HD44780(U) control ASIC wired in reduced (4-bit) mode.

--              All low-level timing of the control signals are handled by this

--               module, allowing client firmware to use a simple register

--               interface to program the LCD panel.

--              Init routine initializes the display and displays a single

--               character to demonstrate correct function, then listens for

--               user data on its external interface.

--

-- Register Map

-- Address  Function

-- Offset  Bitfield Description                        Read/Write

-- 0x0     AAAAAAAA LCD Register Write                 (Write-only)

-- 0x1     AAAAAAAA LCD Data Write                     (Write-only)

-- 0x2     AAAAAAAA LCD Contrast                       (Read-Write)

-- 0x3     AAAAAAAA LCD Backlight                      (Read-Write)

--

--------------------------------------------------------------------------------

-- LCD Controller

--------------------------------------------------------------------------------

--

-- LCD Instruction Set

-- Instruction             RS  RW  D7  D6  D5  D4  D3  D2  D1  D0  Time

------------------------------------------------------------------------

-- Clear Display         | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1.52mS

-- Return Home           | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | x | 1.52mS

-- Entry Mode            | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | ID| S |   37uS

-- Display Pwr           | 0 | 0 | 0 | 0 | 0 | 0 | 1 | D | C | B |   37uS

-- Cursor/Display Shift  | 0 | 0 | 0 | 0 | 0 | 1 | SC| RL| x | x |   37uS

-- Function Set          | 0 | 0 | 0 | 0 | 1 | DL| N | F | x | x |   37uS

-- Set CGRAM Address     | 0 | 0 | 0 | 1 | A | A | A | A | A | A |   37uS

-- Set DDRAM Address     | 0 | 0 | 1 | A | A | A | A | A | A | A |   37uS

-- Notes:

-- ID = Increment/Decrement DDRAM Address (1 = increment, 0 = decrement)

-- S  = Shift Enable (1 = Shift display according to ID, 0 = Don't shift)

-- D  = Display On/Off (1 = on, 0 = off)

-- C  = Cursor On/Off  (1 = on, 0 = off)

-- B  = Cursor Blink   (1 = block cursor, 0 = underline cursor)

-- SC / RL = Shift Cursor/Display Right/Left (see data sheet - not needed for init)

-- F  = Font (0 = 5x8, 1 = 5x11) Ignored on 2-line displays (N = 1)

-- N  = Number of Lines (0 = 1 lines, 1 = 2 lines)

-- DL = Data Length (0 = 4-bit bus, 1 = 8-bit bus) This is fixed at 1 in this module

-- A  = Address (see data sheet for usage)

--

-- Revision History

-- Author          Date     Change

------------------ -------- ---------------------------------------------------

-- Seth Henry      01/22/13 Design Start

-- Seth Henry      04/10/20 Code & comment cleanup

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

library work;

use work.open8_pkg.all;

entity o8_hd44780_4b is

generic(

  Use_Contrast          : boolean;

  Default_Contrast      : std_logic_vector(7 downto 0);

  Use_Backlight         : boolean;

  Default_Brightness    : std_logic_vector(7 downto 0);

  Address               : ADDRESS_TYPE;

  Reset_Level           : std_logic;

  Sys_Freq              : real

);

port(

  Clock                 : in  std_logic;

  Reset                 : in  std_logic;

  --

  uSec_Tick             : in  std_logic;

  --

  Bus_Address           : in  ADDRESS_TYPE;

  Wr_Enable             : in  std_logic;

  Wr_Data               : in  DATA_TYPE;

  Rd_Enable             : in  std_logic;

  Rd_Data               : out DATA_TYPE;

  Interrupt             : out std_logic;

  --

  LCD_E                 : out std_logic;

  LCD_RW                : out std_logic;

  LCD_RS                : out std_logic;

  LCD_D                 : out std_logic_vector(7 downto 4);

  LCD_CN                : out std_logic;

  LCD_BL                : out std_logic

);

end entity;

architecture behave of o8_hd44780_4b is

  constant User_Addr    : std_logic_vector(15 downto 2)

                          := Address(15 downto 2);

  alias  Comp_Addr      is Bus_Address(15 downto 2);

  signal Addr_Match     : std_logic := '0';

  alias  Reg_Addr        is Bus_Address(1 downto 0);

  signal Reg_Addr_q     : std_logic_vector(1 downto 0) := (others => '0');

  signal Wr_En          : std_logic := '0';

  signal Wr_Data_q      : DATA_TYPE := x"00";

  signal Rd_En          : std_logic := '0';

  signal Reg_Valid      : std_logic := '0';

  signal Reg_Sel        : std_logic := '0';

  signal Reg_Data       : std_logic_vector(7 downto 0) := x"00";

  signal Tx_Ready       : std_logic := '0';

  constant LCD_CONFIG1  : std_logic_vector(7 downto 4) := x"3";  -- Init to 4-bit mode

  constant LCD_CONFIG2  : std_logic_vector(7 downto 0) := x"28"; -- Set 4-bit, 2-line mode

  constant LCD_CONFIG3  : std_logic_vector(7 downto 0) := x"0C"; -- Turn display on, no cursor

  constant LCD_CONFIG4  : std_logic_vector(7 downto 0) := x"01"; -- Clear display

  constant LCD_CONFIG5  : std_logic_vector(7 downto 0) := x"06"; -- Positive increment, no shift

  constant LCD_CONFIG6  : std_logic_vector(7 downto 0) := x"2A"; -- Print a "*"

  constant LCD_CONFIG7  : std_logic_vector(7 downto 0) := x"02"; -- Reset the cursor

  signal init_count     : std_logic_vector(2 downto 0) := (others => '0');

  constant INIT_40MS    : integer := 40000;

  constant INIT_BITS    : integer := ceil_log2(INIT_40MS);

  constant INIT_DELAY   : std_logic_vector(INIT_BITS-1 downto 0) :=

                          conv_std_logic_vector(INIT_40MS,INIT_BITS);

-- For "long" instructions, such as clear display and return home, we need to wait for more

--  than 1.52mS. Experimentally, 2mS seems to work ideally, and for init this isn't an issue

  constant CLDSP_2MS    : integer := 2000;

  constant CLDSP_DELAY  : std_logic_vector(INIT_BITS-1 downto 0) :=

                          conv_std_logic_vector(CLDSP_2MS,INIT_BITS);

 -- For some reason, we are required to wait 80uS before checking the busy flag, despite

 --  most instructions completing in 37uS. No clue as to why, but it works

  constant BUSY_50US    : integer := 50;

  constant BUSY_DELAY   : std_logic_vector(INIT_BITS-1 downto 0) :=

                          conv_std_logic_vector(BUSY_50US-1, INIT_BITS);

  signal busy_timer     : std_logic_vector(INIT_BITS-1 downto 0);

  constant SNH_600NS    : integer := integer(Sys_Freq * 0.000000600);

  constant SNH_BITS     : integer := ceil_log2(SNH_600NS);

  constant SNH_DELAY    : std_logic_vector(SNH_BITS-1 downto 0) :=

                          conv_std_logic_vector(SNH_600NS-1, SNH_BITS);

  signal io_timer       : std_logic_vector(SNH_BITS - 1 downto 0) :=

                          (others => '0');

  type IO_STATES is (INIT, PWR_WAIT, INIT_S1, INIT_H1,

                     INIT_WAIT, FN_JUMP, IDLE,

                                                   WR_PREP, WR_SETUP_UB, WR_HOLD_UB, WR_SETUP_LB, WR_HOLD_LB,

                     BUSY_PREP, BUSY_WAIT,

                     ISSUE_INT );

  signal io_state       : IO_STATES := INIT;

  signal LCD_Data       : std_logic_vector(7 downto 0) := x"00";

  signal LCD_Addr       : std_logic := '0';

--------------------------------------------------------------------------------

-- Backlight & Contrast signals

--------------------------------------------------------------------------------

  -- Do not adjust alone! DELTA constants must be

  --  changed as well.

  constant DAC_Width    : integer := 8;

  constant DELTA_1_I    : integer := 1;

  constant DELTA_2_I    : integer := 5;

  constant DELTA_3_I    : integer := 25;

  constant DELTA_4_I    : integer := 75;

  constant DELTA_5_I    : integer := 125;

  constant DELTA_6_I    : integer := 195;

  constant DELTA_1      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_1_I, DAC_Width);

  constant DELTA_2      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_2_I, DAC_Width);

  constant DELTA_3      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_3_I, DAC_Width);

  constant DELTA_4      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_4_I, DAC_Width);

  constant DELTA_5      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_5_I, DAC_Width);

  constant DELTA_6      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_6_I, DAC_Width);

  constant MAX_PERIOD   : integer := 2**DAC_Width;

  constant DIV_WIDTH    : integer := DAC_Width * 2;

  constant PADJ_1_I     : integer := DELTA_1_I * MAX_PERIOD;

  constant PADJ_2_I     : integer := DELTA_2_I * MAX_PERIOD;

  constant PADJ_3_I     : integer := DELTA_3_I * MAX_PERIOD;

  constant PADJ_4_I     : integer := DELTA_4_I * MAX_PERIOD;

  constant PADJ_5_I     : integer := DELTA_5_I * MAX_PERIOD;

  constant PADJ_6_I     : integer := DELTA_6_I * MAX_PERIOD;

  constant PADJ_1       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_1_I,DIV_WIDTH);

  constant PADJ_2       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_2_I,DIV_WIDTH);

  constant PADJ_3       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_3_I,DIV_WIDTH);

  constant PADJ_4       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_4_I,DIV_WIDTH);

  constant PADJ_5       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_5_I,DIV_WIDTH);

  constant PADJ_6       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_6_I,DIV_WIDTH);

  constant CB           : integer := ceil_log2(DIV_WIDTH);

  signal LCD_Contrast   : std_logic_vector(7 downto 0) := x"00";

  signal CN_DACin_q     : std_logic_vector(DAC_WIDTH-1 downto 0) := (others => '0');

  signal CN_Divisor     : std_logic_vector(DIV_WIDTH-1 downto 0) := (others => '0');

  signal CN_Dividend    : std_logic_vector(DIV_WIDTH-1 downto 0) := (others => '0');

  signal CN_q           : std_logic_vector(DIV_WIDTH*2-1 downto 0) := (others => '0');

  signal CN_diff        : std_logic_vector(DIV_WIDTH downto 0) := (others => '0');

  signal CN_count       : std_logic_vector(CB-1 downto 0) := (others => '0');

  signal CN_Next_Wdt    : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal CN_Next_Per    : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal CN_PWM_Wdt     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal CN_PWM_Per     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal CN_Wdt_Ctr     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal CN_Per_Ctr     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal LCD_Bright     : std_logic_vector(7 downto 0) := (others => '0');

  signal BL_DACin_q     : std_logic_vector(DAC_WIDTH-1 downto 0) := (others => '0');

  signal BL_Divisor     : std_logic_vector(DIV_WIDTH-1 downto 0) := (others => '0');

  signal BL_Dividend    : std_logic_vector(DIV_WIDTH-1 downto 0) := (others => '0');

  signal BL_q           : std_logic_vector(DIV_WIDTH*2-1 downto 0) := (others => '0');

  signal BL_diff        : std_logic_vector(DIV_WIDTH downto 0) := (others => '0');

  signal BL_count       : std_logic_vector(CB-1 downto 0) := (others => '0');

  signal BL_Next_Wdt    : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal BL_Next_Per    : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal BL_PWM_Wdt     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal BL_PWM_Per     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal BL_Wdt_Ctr     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

  signal BL_Per_Ctr     : std_logic_vector(DAC_Width-1 downto 0) := (others => '0');

begin

--------------------------------------------------------------------------------

-- Open8 Register interface

--------------------------------------------------------------------------------

  Addr_Match            <= '1' when Comp_Addr = User_Addr else '0';

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Reg_Addr_q        <= (others => '0');

      Wr_Data_q         <= (others => '0');

      Wr_En             <= '0';

      Rd_En             <= '0';

      Rd_Data           <= OPEN8_NULLBUS;

      Reg_Valid         <= '0';

      Reg_Sel           <= '0';

      Reg_Data          <= x"00";

      LCD_Contrast      <= Default_Contrast;

      LCD_Bright        <= Default_Brightness;

    elsif( rising_edge( Clock ) )then

      Reg_Addr_q        <= Reg_Addr;

      Wr_Data_q         <= Wr_Data;

      Wr_En             <= Addr_Match and Wr_Enable;

      Reg_Valid         <= '0';

      if( Wr_En = '1' )then

        case( Reg_Addr_q )is

          when "00" | "01" =>

            Reg_Valid   <= '1';

            Reg_Sel     <= Reg_Addr_q(0);

            Reg_Data    <= Wr_Data_q;

          when "10" =>

            LCD_Contrast<= Wr_Data_q;

          when "11" =>

            LCD_Bright  <= Wr_Data_q;

          when others => null;

        end case;

      end if;

      Rd_Data           <= OPEN8_NULLBUS;

      Rd_En             <= Addr_Match and Rd_Enable;

      if( Rd_En = '1' )then

        case( Reg_Addr_q )is

          when "00" | "01" =>

            Rd_Data(7)  <= Tx_Ready;

          when "10" =>

            Rd_Data     <= LCD_Contrast;

          when "11" =>

            Rd_Data     <= LCD_Bright;

          when others => null;

        end case;

      end if;

    end if;

  end process;

--------------------------------------------------------------------------------

-- LCD and Register logic

--------------------------------------------------------------------------------

  LCD_RW                <= '0'; -- Permanently wire the RW line low

  LCD_IO: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      io_state          <= INIT;

      init_count        <= (others => '0');

      io_timer          <= (others => '0');

      busy_timer        <= (others => '0');

      LCD_Data          <= (others => '0');

      LCD_Addr          <= '0';

      LCD_E             <= '0';

      LCD_RS            <= '0';

      LCD_D             <= (others => '0');

      Tx_Ready          <= '0';

      Interrupt         <= '0';

    elsif( rising_edge(Clock) )then

      LCD_E             <= '0';

      LCD_RS            <= '0';

      LCD_D             <= (others => '0');

      Tx_Ready          <= '0';

      Interrupt         <= '0';

      io_timer          <= io_timer - 1;

      busy_timer        <= busy_timer - uSec_Tick;

      case( io_state )is

        when INIT =>

          busy_timer    <= INIT_DELAY;

          init_count    <= (others => '1');

          io_state      <= PWR_WAIT;

        -- We wait for at least 40mS before continuing initalization.

        when PWR_WAIT =>

          if( busy_timer = 0 )then

            io_timer    <= SNH_DELAY;

            io_state    <= INIT_S1;

          end if;

        -- We write out the first init byte as if we were using an 8-bit

        --  data bus, with a single cycle. This is an exception, and the

        --  rest of the commands are sent using 2-cycle transfers.

        when INIT_S1 =>

          LCD_D         <= LCD_CONFIG1;

          LCD_E         <= '1';

          if( io_timer = 0 )then

            io_timer    <= SNH_DELAY;

            io_state    <= INIT_H1;

          end if;

        when INIT_H1 =>

          LCD_D         <= LCD_CONFIG1;

          if( io_timer = 0 )then

            busy_timer  <= BUSY_DELAY;

            io_state    <= INIT_WAIT;

          end if;

        when INIT_WAIT =>

          if( busy_timer = 0 )then

            io_state    <= FN_JUMP;

          end if;

        when FN_JUMP =>

          io_state      <= WR_PREP;

          case( init_count )is

            when "000" =>

              io_state  <= IDLE;

            when "001" =>

              LCD_Addr  <= '0';

              LCD_Data  <= LCD_CONFIG7; -- Reset the Cursor

            when "010" =>

              LCD_Addr  <= '1';         -- Print a "*", and

              LCD_Data  <= LCD_CONFIG6; --  set RS to 1

            when "011" =>

              LCD_Data  <= LCD_CONFIG5; -- Entry mode

            when "100" =>

              LCD_Data  <= LCD_CONFIG4; -- Clear Display

            when "101" =>

              LCD_Data  <= LCD_CONFIG3; -- Display control

            when "110" | "111" =>

              LCD_Addr  <= '0';

              LCD_Data  <= LCD_CONFIG2; -- Function set

            when others => null;

          end case;

        when IDLE =>

          Tx_Ready      <= '1';

          if( Reg_Valid = '1' )then

            LCD_Addr    <= Reg_Sel;

            LCD_Data    <= Reg_Data;

            io_state    <= WR_PREP;

          end if;

        when WR_PREP =>

          io_timer      <= SNH_DELAY;

          io_state      <= WR_SETUP_UB;

        when WR_SETUP_UB =>

          LCD_RS        <= LCD_Addr;

          LCD_D         <= LCD_Data(7 downto 4);

          LCD_E         <= '1';

          if( io_timer = 0 )then

            io_timer    <= SNH_DELAY;

            io_state    <= WR_HOLD_UB;

          end if;

        when WR_HOLD_UB =>

          LCD_RS        <= LCD_Addr;

          LCD_D         <= LCD_Data(7 downto 4);

          if( io_timer = 0 )then

            LCD_E       <= '0';

            io_timer    <= SNH_DELAY;

            io_state    <= WR_SETUP_LB;

          end if;

        when WR_SETUP_LB =>

          LCD_RS        <= LCD_Addr;

          LCD_D         <= LCD_Data(3 downto 0);

          LCD_E         <= '1';

          if( io_timer = 0 )then

            io_timer    <= SNH_DELAY;

            io_state    <= WR_HOLD_LB;

          end if;

        when WR_HOLD_LB =>

          LCD_RS        <= LCD_Addr;

          LCD_D         <= LCD_Data(3 downto 0);

          if( io_timer = 0 )then

            io_state    <= BUSY_WAIT;

          end if;

        when BUSY_PREP =>

          busy_timer    <= BUSY_DELAY;

          if( LCD_Addr = '0' and LCD_Data < 4 )then

            busy_timer  <= CLDSP_DELAY;

          end if;

          io_state      <= BUSY_WAIT;

        when BUSY_WAIT =>

          if( busy_timer = 0 )then

            io_state    <= ISSUE_INT;

            if( init_count > 0 )then

              init_count<= init_count - 1;

              io_state  <= FN_JUMP;

            end if;

          end if;

        when ISSUE_INT =>

          Interrupt     <= '1';

          io_state      <= IDLE;

        when others => null;

      end case;

    end if;

  end process;

--------------------------------------------------------------------------------

-- Contrast control logic (optional)

--------------------------------------------------------------------------------

Contrast_Disabled: if( not Use_Contrast )generate

  LCD_CN                <= '0';

end generate;

Contrast_Enabled: if( Use_Contrast )generate

  CN_diff               <= ('0' & CN_q(DIV_WIDTH*2-2 downto DIV_WIDTH-1)) -

                           ('0' & CN_Divisor);

  CN_Dividend<= PADJ_2 when CN_DACin_q >= DELTA_2_I and CN_DACin_q < DELTA_3_I else

                PADJ_3 when CN_DACin_q >= DELTA_3_I and CN_DACin_q < DELTA_4_I else

                PADJ_4 when CN_DACin_q >= DELTA_4_I and CN_DACin_q < DELTA_5_I else

                PADJ_5 when CN_DACin_q >= DELTA_5_I and CN_DACin_q < DELTA_6_I else

                PADJ_6 when CN_DACin_q >= DELTA_6_I else

                PADJ_1;

  CN_Next_Wdt<= DELTA_1 when CN_DACin_q >= DELTA_1_I and CN_DACin_q < DELTA_2_I else

                DELTA_2 when CN_DACin_q >= DELTA_2_I and CN_DACin_q < DELTA_3_I else

                DELTA_3 when CN_DACin_q >= DELTA_3_I and CN_DACin_q < DELTA_4_I else

                DELTA_4 when CN_DACin_q >= DELTA_4_I and CN_DACin_q < DELTA_5_I else

                DELTA_5 when CN_DACin_q >= DELTA_5_I and CN_DACin_q < DELTA_6_I else

                DELTA_6 when CN_DACin_q >= DELTA_6_I else

                (others => '0');

  CN_Next_Per           <= BL_q(7 downto 0) - 1;

  CN_vDSM_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      CN_q              <= (others => '0');

      CN_count          <= (others => '1');

      CN_Divisor        <= (others => '0');

      CN_DACin_q        <= (others => '0');

      CN_PWM_Wdt        <= (others => '0');

      CN_PWM_Per        <= (others => '0');

      CN_Per_Ctr        <= (others => '0');

      CN_Wdt_Ctr        <= (others => '0');

      LCD_CN            <= '0';

    elsif( rising_edge(Clock) )then

      CN_q              <= CN_diff(DIV_WIDTH-1 downto 0) &

                           CN_q(DIV_WIDTH-2 downto 0) & '1';

      if( CN_diff(DIV_WIDTH) = '1' )then

        CN_q            <= CN_q(DIV_WIDTH*2-2 downto 0) & '0';

      end if;

      CN_count          <= CN_count + 1;

      if( CN_count = DIV_WIDTH )then

        CN_PWM_Wdt      <= CN_Next_Wdt;

        CN_PWM_Per      <= CN_Next_Per;

        CN_DACin_q      <= LCD_Contrast;

        CN_Divisor      <= (others => '0');

        CN_Divisor(DAC_Width-1 downto 0) <= CN_DACin_q;

        CN_q            <= conv_std_logic_vector(0,DIV_WIDTH) & CN_Dividend;

        CN_count        <= (others => '0');

      end if;

      CN_Per_Ctr        <= CN_Per_Ctr - 1;

      CN_Wdt_Ctr        <= CN_Wdt_Ctr - 1;

      LCD_CN            <= '1';

      if( CN_Wdt_Ctr = 0 )then

        LCD_CN          <= '0';

        CN_Wdt_Ctr      <= (others => '0');

      end if;

      if( CN_Per_Ctr = 0 )then

        CN_Per_Ctr      <= CN_PWM_Per;

        CN_Wdt_Ctr      <= CN_PWM_Wdt;

      end if;

    end if;

  end process;

end generate;

--------------------------------------------------------------------------------

-- Backlight control logic (optional)

--------------------------------------------------------------------------------

Backlight_Disabled: if( not Use_Backlight )generate

  LCD_BL                <= '0';

end generate;

Backlight_Enabled: if( Use_Backlight )generate

  BL_diff               <= ('0' & BL_q(DIV_WIDTH*2-2 downto DIV_WIDTH-1)) -

                           ('0' & BL_Divisor);

  BL_Dividend<= PADJ_2 when BL_DACin_q >= DELTA_2_I and BL_DACin_q < DELTA_3_I else

                PADJ_3 when BL_DACin_q >= DELTA_3_I and BL_DACin_q < DELTA_4_I else

                PADJ_4 when BL_DACin_q >= DELTA_4_I and BL_DACin_q < DELTA_5_I else

                PADJ_5 when BL_DACin_q >= DELTA_5_I and BL_DACin_q < DELTA_6_I else

                PADJ_6 when BL_DACin_q >= DELTA_6_I else

                PADJ_1;

  BL_Next_Wdt<= DELTA_1 when BL_DACin_q >= DELTA_1_I and BL_DACin_q < DELTA_2_I else

                DELTA_2 when BL_DACin_q >= DELTA_2_I and BL_DACin_q < DELTA_3_I else

                DELTA_3 when BL_DACin_q >= DELTA_3_I and BL_DACin_q < DELTA_4_I else

                DELTA_4 when BL_DACin_q >= DELTA_4_I and BL_DACin_q < DELTA_5_I else

                DELTA_5 when BL_DACin_q >= DELTA_5_I and BL_DACin_q < DELTA_6_I else

                DELTA_6 when BL_DACin_q >= DELTA_6_I else

                (others => '0');

  BL_Next_Per           <= BL_q(7 downto 0) - 1;

  BL_vDSM_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      BL_q              <= (others => '0');