sentword.vhd

用硬件VHDL语言实现的串口通信的试验代码

----------------------------------------------------
--芳元电子工作室，版权所有，严禁用于商业用途
--实体名：sentword
--功  能：字符发送控制器，发送"I love you!"
--接  口：clk    -为时钟信号，波特率为clk的1/4
--        tdempty-发送完毕空信号输入
--        wr     -写使能信号
--        qout   -要发送的数据，8bit
--作  者：Justin Xu
--日  期：2005-06-21
----------------------------------------------------

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

entity sentword is
port
(clk     : in  std_logic;
 tdempty : in  std_logic;
 wr      : out std_logic:='1';
 qout    : out std_logic_vector(7 downto 0)
);
end sentword;

architecture behave of sentword is
type state_type is (s0,s1,s2,s3,s4,s5,s6,s7,s8,s9,s10,s11,s12,s13,s14,s15,s16);
signal state:state_type:=s0;
begin
  process(clk)
  begin
    if clk'event and clk='1' then
         case state is
           when s0=>--wr<='0';           
                    qout<="00000000";
                    if tdempty='1' then
                       state<=s1;
                       wr<='0';
                    else
                       state<=s0;
                       wr<='1';
                    end if;
           when s1=>--wr<='0';          
                    qout<="00000000";
                    if tdempty='1' then
                       state<=s2;
                       wr<='0';
                    else
                       state<=s1;
                       wr<='1';
                    end if;
           when s2=>--wr<='0';             --发送‘I’
                    qout<="01001001";
                    if tdempty='1' then
                       state<=s3;
                       wr<='0';
                    else
                       state<=s2;
                       wr<='1';
                    end if;
           when s3=>--wr<='1';             --发送空格
                    qout<="00100000";
                    if tdempty='1' then
                       state<=s4;
                       wr<='0';
                    else
                       state<=s3;
                       wr<='1';
                    end if;
           when s4=>--wr<='1';             --发送‘l’
                    qout<="01101100";
                    if tdempty='1' then
                       state<=s5;
                       wr<='0';
                    else
                       state<=s4;
                       wr<='1';
                    end if;
           when s5=>--wr<='1';             --发送‘o’
                    qout<="01101111";
                    if tdempty='1' then
                       state<=s6;
                       wr<='0';
                    else
                       state<=s5;
                       wr<='1';
                    end if;
           when s6=>--wr<='1';             --发送‘v’
                    qout<="01110110";
                    if tdempty='1' then
                       state<=s7;
                       wr<='0';
                    else
                       state<=s6;
                       wr<='1';
                    end if;
           when s7=>--wr<='1';             --发送‘e’
                    qout<="01100101";
                    if tdempty='1' then
                       state<=s8;
                       wr<='0';
                    else
                       state<=s7;
                       wr<='1';
                    end if;
           when s8=>--wr<='1';             --发送空格
                    qout<="00100000";
                    if tdempty='1' then
                       state<=s9;
                       wr<='0';
                    else
                       state<=s8;
                       wr<='1';
                    end if;
           when s9=>--wr<='1';             --发送‘y’
                    qout<="01111001";
                    if tdempty='1' then
                       state<=s10;
                       wr<='0';
                    else
                       state<=s9;
                       wr<='1';
                    end if;
           when s10=>--wr<='1';             --发送‘o’
                    qout<="01101111";
                    if tdempty='1' then
                       state<=s11;
                       wr<='0';
                    else
                       state<=s10;
                       wr<='1';
                    end if;
           when s11=>--wr<='1';            --发送‘u’
                    qout<="01110101";
                    if tdempty='1' then
                       state<=s12;
                       wr<='0';
                    else
                       state<=s11;
                       wr<='1';
                    end if;
           when s12=>--wr<='1';            --发送‘！’
                    qout<="00100001";
                    if tdempty='1' then
                       state<=s13;
                       wr<='0';
                    else
                       state<=s12;
                       wr<='1';
                    end if;
           when s13=>--wr<='1';            --发送空格
                    qout<="00100000";
                    if tdempty='1' then
                       state<=s2;
                       wr<='0';
                    else
                       state<=s13;
                       wr<='1';
                    end if;
           when others=>state<=s1;
                        wr<='0';
                        qout<="00000000";
         end case;                     
    end if;
  end process;
end behave;