vhdl实现uart程序

下面是一个简单的 VHDL 代码实现 UART 的例子程序：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity UART_Test is
    Port ( CLK: in std_logic;
           RST: in std_logic;
           RX: in std_logic;
           TX: out std_logic);
end UART_Test;

architecture Behavioral of UART_Test is
    signal TX_busy : std_logic := '0';
    signal TX_data : std_logic_vector(7 downto 0);
    signal TX_counter : integer range 0 to 11 := 0;

    signal RX_data : std_logic_vector(7 downto 0);
    signal RX_counter : integer range 0 to 11 := 0;
    signal RX_busy : std_logic := '0';
    signal RX_done : std_logic := '0';

    constant BAUD_RATE : integer := 9600;
    constant CLK_FREQ : integer := 50000000; -- 50 MHz clock

begin

    UART_TX : process(CLK, RST)
    begin
        if(RST = '1') then
            TX_busy <= '0';
            TX_data <= (others => '0');
            TX_counter <= 0;
        elsif(CLK'event and CLK = '1') then
            if(TX_busy = '1') then
                TX_counter <= TX_counter + 1;
                if(TX_counter = 11) then
                    TX_data <= (others => '0');
                    TX_busy <= '0';
                    TX_counter <= 0;
                end if;
            else
                if(RX_done = '1') then
                    TX_data <= RX_data;
                    TX_busy <= '1';
                    RX_done <= '0';
                    TX_counter <= 0;
                end if;
            end if;
        end if;
    end process UART_TX;

    UART_RX : process(CLK, RST)
    begin
        if(RST = '1') then
            RX_busy <= '0';
            RX_data <= (others => '0');
            RX_counter <= 0;
        elsif(CLK'event and CLK = '1') then
            if(RX_busy = '1') then
                RX_counter <= RX_counter + 1;
                if(RX_counter = 11) then
                    RX_done <= '1';
                    RX_busy <= '0';
                    RX_counter <= 0;
                end if;
            else
                if(RX = '0') then
                    RX_busy <= '1';
                    RX_counter <= 0;
                end if;
            end if;
        end if;
    end process UART_RX;

    -- Baud rate generator
    UART_BAUD : process(CLK, RST)
    variable baud_counter : integer range 0 to round(CLK_FREQ / (BAUD_RATE * 16)) - 1;
    begin
        if(RST = '1') then
            baud_counter := 0;
        elsif(CLK'event and CLK = '1') then
            baud_counter := baud_counter + 1;
            if(baud_counter = round(CLK_FREQ / (BAUD_RATE * 16)) - 1) then
                baud_counter := 0;
            end if;
        end if;

        if(baud_counter = 0) then
            TX <= TX_data(TX_data'high);
            TX_data <= TX_data(TX_data'high - 1 downto 0) & '0';
        else
            TX <= '1';
        end if;
    end process UART_BAUD;

end Behavioral;

该程序包括了一个简单的波特率生成器和 TX 和 RX 的状态机。在该程序中，当接收到数据后，它会被发送回去。该实现使用9600波特率，50 MHz时钟频率和8个数据位。为了测试该程序，你可以将一个串口转USB适配器连接到计算机上，然后将TX和RX引脚连接到适配器的TX和RX引脚上，就可以在计算机上使用串口工具来测试UART程序了。