lcd.vhd

关于lcd的vhdl程序代码

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all; 
use ieee.std_logic_unsigned.all;


entity lcd is 
	generic ( asciiwidth : positive := 8);
	
	port (	clk       : in std_logic;
			reset      : in std_logic;  -- active low
			data_valid : in std_logic;  -- enables lcd to start new write cycle when high

		    ------interface to LCM----------------------------------------------
			lcd_data   : out std_logic_vector(asciiwidth-1 downto 0);
			lcd_select : out std_logic;  -- selects data(0) or instruction(1)
			lcd_rw,tt     : out std_logic;  -- read (1) or write (0) data
			lcd_enable : out std_logic;  -- must be pulsed at clock frequency
			
			---------------------------------------------------------------------
			
			done       : out std_logic);  -- set low during write cycle, high if ready for new data
end lcd;                                  

architecture behavioural of lcd is

constant countwidth : positive := 3;

type state_type is (warmup, setfunc, dispoff, clear, setmode, home, idle, write);

signal state : state_type;
signal rw_int, enable_int : std_logic;
signal count : std_logic_vector(countwidth downto 0);
signal write_mode : std_logic;       -- stores whether to enter write cycle after clearing display
signal last_data_valid : std_logic;  -- used to track rising edge on valid


begin
	tt<='0';
	lcd_rw <= rw_int;
	lcd_enable <= enable_int;
	enable_int <= not clk;  -- this is very important! if enable is not pulsed, lcd will not write
	

	state_set: process (clk, reset)
	begin
		if reset = '0' then
			count <= (others => '0');
			write_mode <= '1';
			state <= warmup;
			
		elsif (clk'event and clk = '1') then
			case state is
				when warmup =>
					
					lcd_select <= '0';
					rw_int <= '0';
					done <= '0';  
					lcd_data <= "00000000";  -- do nothing
					if count = "0111" then
						count <= (others => '0');
						state <= setfunc;
					else
						count <= count + '1';
						state <= warmup;
					end if;
					
				when setfunc =>
					lcd_data <= "00110000";
					if count = "1111" then
						state <= dispoff;
					else
						count <= count + '1';
						state <= setfunc;
					end if;
					
				when dispoff =>
					lcd_data <= "00001000";
					count <= (others => '0');
					state <= clear;
					
				when clear =>
					lcd_data <= "00000001";  -- clear display
					if count = "0101" then
						state <= setmode;
					else
						count <= count + '1';
						state <= clear;
					end if;
					
				when setmode =>
					lcd_data <= "00000110";
					count <= (others => '0');
					state <= home;
					
				when home =>
					lcd_data <= "00001100";
					if count = "0100" then
						if write_mode = '0' then
						  done <= '1';
						  state <= idle;
						else
						  done <= '0';
						  count <= (others => '0');
						  state <= write;
						end if;
					else
						count <= count + '1';
						state <= home;
					end if;	
            
				when idle =>
					
					if data_valid = '1' and last_data_valid = '0' then
						last_data_valid <= '1';
						count <= (others => '0');
						done <= '0';
						write_mode <= '1';
						state <= clear;
					else
						if data_valid = '0' then
							last_data_valid <= '0';
						end if;
						lcd_data <= (others => '0');
						done <= '1';
						state <= idle;
					end if;
					
					
				when write =>
									
						
							CASE count IS
								WHEN "0000" =>
						    		lcd_data <= "00100000";  -- ' '						    		
								WHEN "0001" =>
							    	lcd_data <= "00100000";  -- ' '
							    WHEN "0010" =>
							    	lcd_data <= "01110100";  -- 't'
							    WHEN "0011" =>
						    		lcd_data <= "01100101";  -- 'e'
							    WHEN "0100" =>
							    	lcd_data <= "01110011";  -- 's'
							    WHEN "0101" =>
							    	lcd_data <= "01110100";  -- 't'
							    WHEN "0110" =>
							    	lcd_data <= "01101001";  -- 'i'
							    WHEN "0111" =>
							    	lcd_data <= "01101110";  -- 'n '
							    WHEN "1000" =>
							    	lcd_data <= "01100111";  -- 'g'
							    WHEN "1001" =>
							    	lcd_data <= "00100000";  -- ' '
							    WHEN "1010" =>
							    	lcd_data <= "01101110";  -- 'n'
							    WHEN "1011" =>
							    	lcd_data <= "01101111";  -- 'o'
							    WHEN "1100" =>
							    	lcd_data <= "01110111";  -- 'w'

							    WHEN "1101" =>
							    	lcd_data <= "00100001";  -- '!'
							    WHEN "1110" =>
							    	lcd_data <= "00100000";  -- ' '
							    WHEN "1111" =>
							     	lcd_data <= "00100000";  -- ' '
							    WHEN OTHERS =>
							    	lcd_data <= "00100000";  -- ' '
							END CASE;
			
						lcd_select <= '1';
						count <= count + '1';
					    state <= write;
					
					      
					
			end case;
		end if;
	end process;
	
	
	
end behavioural;