-- 本模塊的功能是驗證實現和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試工具來驗證程序的功能。
-- 程序實現了一個收發一幀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個數據位，1個結束
--位。串口的波特律由程序中定義的div_par參數決定，更改該參數可以實
--現相應的波特率。程序當前設定的div_par 的值是0x104，對應的波特率是
--9600。用一個8倍波特率的時鐘將發送或接受每一位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：串口處於全雙工工作狀態，按動key2，CPLD向PC發送?elcome"
--字元串（串口調試工具設成按ASCII碼接受方式）；PC可隨時向CPLD發送0-F的十六進位
--數據，CPLD接受后顯示在7段數碼管上。
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; --串列數據接收端
txd : OUT std_logic; --串列數據發送端
en : OUT std_logic_vector(7 downto 0); -- 數碼管使能
seg_data : OUT std_logic_vector(7 DOWNTO 0); --數碼管數據
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);--該寄存器的計數值對應發送時當前位於的時隙數
SIGNAL div8_rec_reg : std_logic_vector(2 DOWNTO 0); --寄存器的計數值對應接收時當前位於的時隙數
SIGNAL state_tras : std_logic_vector(3 DOWNTO 0); -- 發送狀態寄存器
SIGNAL state_rec : std_logic_vector(3 DOWNTO 0); -- 接受狀態寄存器
SIGNAL clkbaud_tras : std_logic; --以波特率為頻率的發送使能信號
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; -- 開始發送標誌
SIGNAL recstart_tmp : std_logic; --開始接受標誌
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，因為接收數據為非同步信號，故用兩級緩存
SIGNAL txd_reg : std_logic; --發送寄存器
SIGNAL rxd_buf : std_logic_vector(7 DOWNTO 0);--接受數據緩存
SIGNAL txd_buf : std_logic_vector(7 DOWNTO 0);--發送數據緩存
SIGNAL send_state : std_logic_vector(2 DOWNTO 0);--每次按鍵給PC發送"Welcome"字元串，這是發送狀態寄存器
SIGNAL cnt_delay : std_logic_vector(19 DOWNTO 0);--延時去抖計數器
SIGNAL start_delaycnt : std_logic; --開始延時計數標誌
SIGNAL key_entry1 : std_logic; --確定有鍵按下曛?
SIGNAL key_entry2 : std_logic; --確定有鍵按下標誌
--//////////////////////////////////////////////
CONSTANT div_par : std_logic_vector(15 DOWNTO 0) := "0000000100000100";
--分頻參數，其值由對應的波特率計算而得，按此參數分頻的時鐘頻率是波倍特率的8倍，此處值對應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 --接收開始標誌
div8_rec_reg <= div8_rec_reg + "001";--接收開始后，時隙數在8倍波特率的時鐘下加1循環
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";--發送開始后，時隙數在8倍波特率的時鐘下加1循環
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，發送使能信號有效，將數據發出
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機的數據
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
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) --將接受的數據用數碼管顯示出來
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;
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