uart.vhd

一个完整的用cpld实现串口功能的代码。经过验证

            CASE state_tras IS
               WHEN "0000" =>  --发送起始位
                        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" => --发送第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" =>  --发送第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" =>  --发送第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" => --发送第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" => --发送第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" => --发送第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" => --发送第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" =>  --发送第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" =>  --发送停止位
                        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机的数据
   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 --检测到起始位的下降沿，进入接受状态
                  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)   --将接受的数据用数码管显示出来
   BEGIN
      CASE rxd_buf IS
         WHEN "00110000" =>
                  seg_data <= "00000011";    
         WHEN "00110001" =>
                  seg_data <= "10011111";    
         WHEN "00110010" =>
                  seg_data <= "00100101";    
         WHEN "00110011" =>
                  seg_data <= "00001101";    
         WHEN "00110100" =>
                  seg_data <= "10011001";    
         WHEN "00110101" =>
                  seg_data <= "01001001";    
         WHEN "00110110" =>
                  seg_data <= "01000001";    
         WHEN "00110111" =>
                  seg_data <= "00011111";    
         WHEN "00111000" =>
                  seg_data <= "00000001";    
         WHEN "01000001" =>
                  seg_data <= "00011001";    
         WHEN "01000010" =>
                  seg_data <= "00010001";    
         WHEN "01000011" =>
                  seg_data <= "11000001";    
         WHEN "01000100" =>
                  seg_data <= "01100011";    
         WHEN "01000101" =>
                  seg_data <= "10000101";    
         WHEN "01000110" =>
                  seg_data <= "01100001";    
         WHEN "01000111" =>
                  seg_data <= "01110001";    
         WHEN OTHERS  =>
                  seg_data <= "11111111";    
      
      END CASE;
   END PROCESS;

END arch;