VHDL設(shè)計的串口通信程序

本模塊的功能是驗證實現(xiàn)和PC機進行基本的串口通信的功能。需要在
PC機上安裝一個串口調(diào)試工具來驗證程序的功能。
程序?qū)崿F(xiàn)了一個收發(fā)一幀10個bit（即無奇偶校驗位）的串口控
制器，10個bit是1位起始位，8個數(shù)據(jù)位，1個結(jié)束
位。串口的波特律由程序中定義的div_par參數(shù)決定，更改該參數(shù)可以實
現(xiàn)相應(yīng)的波特率。程序當前設(shè)定的div_par 的值是0x104，對應(yīng)的波特率是
9600。用一個8倍波特率的時鐘將發(fā)送或接受每一位bit的周期時間
劃分為8個時隙以使通信同步.
程序的工作過程是：串口處于全雙工工作狀態(tài)，按動key2，CPLD向PC發(fā)送皐elcome"
字符串（串口調(diào)試工具設(shè)成按ASCII碼接受方式）；PC可隨時向CPLD發(fā)送0-F的十六進制
數(shù)據(jù)，CPLD接受后顯示在7段數(shù)碼管上。
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY UART IS
?? PORT (
????? clk???????????????????? : IN std_logic;??
????? rst???????????????????? : IN std_logic;??
????? rxd???????????????????? : IN std_logic;?? 串行數(shù)據(jù)接收端
????? txd???????????????????? : OUT std_logic; 串行數(shù)據(jù)發(fā)送端?
????? en????????????????????? : OUT std_logic_vector(7 downto 0); 數(shù)碼管使能
????? seg_data??????????????? : OUT std_logic_vector(7 DOWNTO 0); 數(shù)碼管數(shù)據(jù)?
????? key_input?????????????? : IN std_logic? 按鍵輸入
????? );
END UART;

ARCHITECTURE arch OF UART IS
?? //////////////////inner reg////////////////////
?? SIGNAL div_reg????????????????? :? std_logic_vector(15 DOWNTO 0);分頻計數(shù)器，分頻值由波特率決定。分頻后得到頻率8倍波特率的時鐘??
?? SIGNAL div8_tras_reg??????????? :? std_logic_vector(2 DOWNTO 0);該寄存器的計數(shù)值對應(yīng)發(fā)送時當前位于的時隙數(shù)??
?? SIGNAL div8_rec_reg???????????? :? std_logic_vector(2 DOWNTO 0);? 寄存器的計數(shù)值對應(yīng)接收時當前位于的時隙數(shù)
?? SIGNAL state_tras?????????????? :? std_logic_vector(3 DOWNTO 0);? 發(fā)送狀態(tài)寄存器
?? SIGNAL state_rec??????????????? :? std_logic_vector(3 DOWNTO 0); 接受狀態(tài)寄存器
?? SIGNAL clkbaud_tras???????????? :? std_logic; 以波特率為頻率的發(fā)送使能信號?
?? SIGNAL clkbaud_rec????????????? :? std_logic; 以波特率為頻率的接受使能信號?
?? SIGNAL clkbaud8x??????????????? :? std_logic; 以8倍波特率為頻率的時鐘，它的作用是將發(fā)送或接受一個bit的時鐘周期分為8個時隙?
?? SIGNAL recstart???????????????? :? std_logic; 開始發(fā)送標志
?? SIGNAL recstart_tmp???????????? :? std_logic; 開始接受標志?
?? SIGNAL trasstart??????????????? :? std_logic;??
?? SIGNAL rxd_reg1???????????????? :? std_logic; 接收寄存器1?
?? SIGNAL rxd_reg2???????????????? :? std_logic; 接收寄存器2，因為接收數(shù)據(jù)為異步信號，故用兩級緩存?
?? SIGNAL txd_reg????????????????? :? std_logic; 發(fā)送寄存器?
?? SIGNAL rxd_buf????????????????? :? std_logic_vector(7 DOWNTO 0);接受數(shù)據(jù)緩存??
?? SIGNAL txd_buf????????????????? :? std_logic_vector(7 DOWNTO 0);發(fā)送數(shù)據(jù)緩存??
?? SIGNAL send_state?????????????? :? std_logic_vector(2 DOWNTO 0);每次按鍵給PC發(fā)送"Welcome"字符串，這是發(fā)送狀態(tài)寄存器??
?? SIGNAL cnt_delay??????????????? :? std_logic_vector(19 DOWNTO 0);延時去抖計數(shù)器??
?? SIGNAL start_delaycnt?????????? :? std_logic;? 開始延時計數(shù)標志
?? SIGNAL key_entry1?????????????? :? std_logic;? 確定有鍵按下曛?
?? SIGNAL key_entry2?????????????? :? std_logic;? 確定有鍵按下標志
?? //////////////////////////////////////////////
?? CONSTANT? div_par?????????????? :? std_logic_vector(15 DOWNTO 0) := "0000000100000100";
?? 分頻參數(shù)，其值由對應(yīng)的波特率計算而得，按此參數(shù)分頻的時鐘頻率是波倍特率的8倍，此處值對應(yīng)9600的波特率，即分頻出的時鐘頻率是9600*8????
?? SIGNAL txd_xhdl3??????????????? :? std_logic;??

BEGIN
?? en <="01010101" ;7段數(shù)碼管使能信號賦值
?? txd <= txd_xhdl3;??
?? txd_xhdl3 <= txd_reg ;

?? PROCESS(clk,rst)
?? BEGIN
??????
????? IF (NOT rst = ’1’) THEN
???????? cnt_delay <= "00000000000000000000";???
???????? start_delaycnt <= ’0’;???
????? ELSIF(clk’EVENT AND clk=’1’)THEN
???????? IF (start_delaycnt = ’1’) THEN
??????????? IF (cnt_delay /= "11000011010100000000") THEN
?????????????? cnt_delay <= cnt_delay + "00000000000000000001";???
??????????? ELSE
?????????????? cnt_delay <= "00000000000000000000";???
?????????????? start_delaycnt <= ’0’;???
??????????? END IF;
???????? ELSE
??????????? IF ((NOT key_input=’1’) AND (cnt_delay = "00000000000000000000")) THEN
?????????????? start_delaycnt <= ’1’;???
??????????? END IF;
???????? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(clk,rst)
?? BEGIN
??????
????? IF (NOT rst = ’1’) THEN
???????? key_entry1 <= ’0’;???
????? ELSIF(clk’EVENT AND clk=’1’)THEN
???????? IF (key_entry2 = ’1’) THEN
??????????? key_entry1 <= ’0’;???
???????? ELSE
??????????? IF (cnt_delay = "11000011010100000000") THEN
?????????????? IF (NOT key_input = ’1’) THEN
????????????????? key_entry1 <= ’1’;???
?????????????? END IF;
??????????? END IF;
???????? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(clk,rst)
?? BEGIN
??????
????? IF (NOT rst = ’1’) THEN
???????? div_reg <= "0000000000000000";???
????? ELSIF(clk’EVENT AND clk=’1’)THEN
???????? IF (div_reg = div_par - "0000000000000001") THEN
??????????? div_reg <= "0000000000000000";???
???????? ELSE
??????????? div_reg <= div_reg + "0000000000000001";???
???????? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(clk,rst)? 分頻得到8倍波特率的時鐘
?? BEGIN
??????
????? IF (NOT rst = ’1’) THEN
???????? clkbaud8x <= ’0’;???
????? ELSIF(clk’EVENT AND clk=’1’)THEN
???????? IF (div_reg = div_par - "0000000000000001") THEN
??????????? clkbaud8x <= NOT clkbaud8x;???
???????? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(clkbaud8x,rst)
?? BEGIN
????? IF (NOT rst = ’1’) THEN
???????? div8_rec_reg <= "000";???
????? ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
???????? IF (recstart = ’1’) THEN? 接收開始標志
??????????? div8_rec_reg <= div8_rec_reg + "001";接收開始后，時隙數(shù)在8倍波特率的時鐘下加1循環(huán)???
???????? END IF;
??? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(clkbaud8x,rst)
?? BEGIN
????? IF (NOT rst = ’1’) THEN
???????? div8_tras_reg <= "000";???
????? ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
???????? IF (trasstart = ’1’) THEN
??????????? div8_tras_reg <= div8_tras_reg + "001";發(fā)送開始后，時隙數(shù)在8倍波特率的時鐘下加1循環(huán)???
???????? END IF;
??? END IF;
????? END IF;
?? END PROCESS;

?? PROCESS(div8_rec_reg)
?? BEGIN
????? IF (div8_rec_reg = "111") THEN
???????? clkbaud_rec <= ’1’; -在第7個時隙，接收??
????? ELSE
???????? clkbaud_rec <= ’0’;???
????? END IF;
?? END PROCESS;

?? PROCESS(div8_tras_reg)
?? BEGIN
????? IF (div8_tras_reg = "111") THEN
???????? clkbaud_tras <= ’1’;? 在第7個時隙，發(fā)送使能信號有效，將數(shù)據(jù)發(fā)出?
????? ELSE
???????? clkbaud_tras <= ’0’;???
????? END IF;
?? END PROCESS;

?? PROCESS(clkbaud8x,rst)
?? BEGIN
????? IF (NOT rst = ’1’) THEN
???????? txd_reg <= ’1’;???
???????? trasstart <= ’0’;???
???????? txd_buf <= "00000000";???
???????? state_tras <= "0000";???
???????? send_state <= "000";???
???????? key_entry2 <= ’0’;???
????? ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
???????? IF (NOT key_entry2 = ’1’) THEN
??????????? IF (key_entry1 = ’1’) THEN
?????????????? key_entry2 <= ’1’;???
?????????????? txd_buf <= "01110111";?? "w"
??????????? END IF;
???????? ELSE
??????????? CASE state_tras IS
?????????????? WHEN "0000" =>? 發(fā)送起始位
??????????????????????? IF ((NOT trasstart=’1’) AND (send_state < "111") ) THEN
?????????????????????????? trasstart <= ’1’;???
??????????????????????? ELSE
?????????????????????????? IF (send_state < "111") THEN
????????????????????????????? IF (clkbaud_tras = ’1’) THEN
???????????????????????????????? txd_reg <= ’0’;???
???????????????????????????????? state_tras <= state_tras + "0001";???
????????????????????????????? END IF;
?????????????????????????? ELSE
????????????????????????????? key_entry2 <= ’0’;???
????????????????????????????? state_tras <= "0000";???
?????????????????????????? END IF;
??????????????????????? END IF;
?????????????? WHEN "0001" => 發(fā)送第1位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0010" =>? 發(fā)送第2位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0011" =>? 發(fā)送第3位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0100" => 發(fā)送第4位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0101" => 發(fā)送第5位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0110" => 發(fā)送第6位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "0111" => 發(fā)送第7位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "1000" =>? 發(fā)送第8位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= txd_buf(0);???
?????????????????????????? txd_buf(6 DOWNTO 0) <= txd_buf(7 DOWNTO 1);???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "1001" =>? 發(fā)送停止位
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? txd_reg <= ’1’;???
?????????????????????????? txd_buf <= "01010101";???
?????????????????????????? state_tras <= state_tras + "0001";???
??????????????????????? END IF;
?????????????? WHEN "1111" =>
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? state_tras <= state_tras + "0001";???
?????????????????????????? send_state <= send_state + "001";???
?????????????????????????? trasstart <= ’0’;???
?????????????????????????? CASE send_state IS
????????????????????????????? WHEN "000" =>
?????????????????????????????????????? txd_buf <= "01100101"; "e"??
????????????????????????????? WHEN "001" =>
?????????????????????????????????????? txd_buf <= "01101100"; "l"??
????????????????????????????? WHEN "010" =>
?????????????????????????????????????? txd_buf <= "01100011";? "c"?
????????????????????????????? WHEN "011" =>
?????????????????????????????????????? txd_buf <= "01101111"; "o"?
????????????????????????????? WHEN "100" =>
?????????????????????????????????????? txd_buf <= "01101101";? "m"?
????????????????????????????? WHEN "101" =>
?????????????????????????????????????? txd_buf <= "01100101"; "e"??
????????????????????????????? WHEN OTHERS? =>
?????????????????????????????????????? txd_buf <= "00000000";?
?????????????????????????????
?????????????????????????? END CASE;
??????????????????????? END IF;
?????????????? WHEN OTHERS? =>
??????????????????????? IF (clkbaud_tras = ’1’) THEN
?????????????????????????? state_tras <= state_tras + "0001";???
?????????????????????????? trasstart <= ’1’;???
??????????????????????? END IF;
??????????????
??????????? END CASE;
???????? END IF;
????? END IF;
?END IF;
?? END PROCESS;

?? PROCESS(clkbaud8x,rst)? 接受PC機的數(shù)據(jù)
?? BEGIN
????? IF (NOT rst = ’1’) THEN
???????? rxd_reg1 <= ’0’;???
???????? rxd_reg2 <= ’0’;???
???????? rxd_buf <= "00000000";???
???????? state_rec <= "0000";???
???????? recstart <= ’0’;???
???????? recstart_tmp <= ’0’;???
????? ELSE IF(clkbaud8x’EVENT AND clkbaud8x = ’1’) THEN
???????? rxd_reg1 <= rxd;???
???????? rxd_reg2 <= rxd_reg1;???
???????? IF (state_rec = "0000") THEN
??????????? IF (recstart_tmp = ’1’) THEN
?????????????? recstart <= ’1’;???
?????????????? recstart_tmp <= ’0’;???
?????????????? state_rec <= state_rec + "0001";???
??????????? ELSE
?????????????? IF ((NOT rxd_reg1 AND rxd_reg2) = ’1’) THEN 檢測到起始位的下降沿，進入接受狀態(tài)
????????????????? recstart_tmp <= ’1’;???
?????????????? END IF;
??????????? END IF;
???????? ELSE
??????????? IF (state_rec >= "0001" AND state_rec<="1000") THEN
?????????????? IF (clkbaud_rec = ’1’) THEN
????????????????? rxd_buf(7) <= rxd_reg2;???
????????????????? rxd_buf(6 DOWNTO 0) <= rxd_buf(7 DOWNTO 1);???
????????????????? state_rec <= state_rec + "0001";???
?????????????? END IF;
??????????? ELSE
?????????????? IF (state_rec = "1001") THEN
????????????????? IF (clkbaud_rec = ’1’) THEN
???????????????????? state_rec <= "0000";???
???????????????????? recstart <= ’0’;???
????????????????? END IF;
?????????????? END IF;
??????????? END IF;
???????? END IF;
????? END IF;
?END IF;
?? END PROCESS;

?? PROCESS(rxd_buf)?? 將接受的數(shù)據(jù)用數(shù)碼管顯示出來
?? BEGIN
????? CASE rxd_buf IS
???????? WHEN "00110000" =>
????????????????? seg_data <= "00000011"; 0??
???????? WHEN "00110001" =>
????????????????? seg_data <= "10011111"; 1?
???????? WHEN "00110010" =>
????????????????? seg_data <= "00100101"; 2?
???????? WHEN "00110011" =>
????????????????? seg_data <= "00001101"; 3??????
???????? WHEN "00110100" =>
????????????????? seg_data <= "10011001"; 4??
&nbs p;??????? WHEN "00110101" =>
????????????????? seg_data <= "01001001"; 5?
???????? WHEN "00110110" =>
????????????????? seg_data <= "01000001"; 6??
???????? WHEN "00110111" =>
????????????????? seg_data <= "00011111"; 7??
???????? WHEN "00111000" =>
????????????????? seg_data <= "00000001"; 8???
???????? WHEN "00111001" =>
????????????????? seg_data <= "00001001"; 9??
???????? WHEN "01000001" =>
????????????????? seg_data <= "00010001"; A??
???????? WHEN "01000010" =>
????????????????? seg_data <= "11000001"; B??
???????? WHEN "01000011" =>
????????????????? seg_data <= "01100011"; C??
???????? WHEN "01000100" =>
????????????????? seg_data <= "10000101"; D?
???????? WHEN "01000101" =>
????????????????? seg_data <= "01100001"; E??
???????? WHEN "01000110" =>
????????????????? seg_data <= "01110001"; F???
???????? WHEN OTHERS? =>
????????????????? seg_data <= "11111111";??????????
????? END CASE;
?? END PROCESS;
END arch;