VHDL实现RS422接收模块的简单示例代码

用VHDL生成RS422接受模块

好的，下面是一个简单的VHDL代码示例，用于实现一个RS422接收模块。RS422是一种差分信号标准，通常用于长距离和高噪声环境中的串行通信。这个示例假设你已经有一个差分信号转换器，将RS422信号转换为单端信号。

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity RS422_Receiver is
    Port (
        clk         : in  std_logic;  -- System clock
        rst         : in  std_logic;  -- System reset
        rs422_in    : in  std_logic;  -- RS422 input signal (single-ended after conversion)
        data_out    : out std_logic_vector(7 downto 0);  -- 8-bit data output
        data_valid  : out std_logic  -- Data valid signal
    );
end RS422_Receiver;

architecture Behavioral of RS422_Receiver is
    signal bit_counter : integer range 0 to 9 := 0;  -- Bit counter (1 start bit + 8 data bits + 1 stop bit)
    signal shift_reg   : std_logic_vector(7 downto 0) := (others => '0');  -- Shift register for received data
    signal receiving   : std_logic := '0';  -- Receiving flag
    signal clk_div     : integer := 0;  -- Clock divider for baud rate generation
    constant BAUD_RATE_DIV : integer := 10416;  -- Clock divider value for 9600 baud rate (assuming 100 MHz clock)
begin
    process(clk, rst)
    begin
        if rst = '1' then
            bit_counter <= 0;
            shift_reg <= (others => '0');
            receiving <= '0';
            clk_div <= 0;
            data_valid <= '0';
        elsif rising_edge(clk) then
            if clk_div = BAUD_RATE_DIV then
                clk_div <= 0;
                if receiving = '1' then
                    if bit_counter = 0 then
                        if rs422_in = '0' then  -- Start bit detected
                            bit_counter <= bit_counter + 1;
                        end if;
                    elsif bit_counter < 9 then
                        shift_reg <= rs422_in & shift_reg(7 downto 1);  -- Shift in data bits
                        bit_counter <= bit_counter + 1;
                    else
                        if rs422_in = '1' then  -- Stop bit detected
                            data_out <= shift_reg;
                            data_valid <= '1';
                        end if;
                        bit_counter <= 0;
                        receiving <= '0';
                    end if;
                else
                    if rs422_in = '0' then  -- Start bit detected
                        receiving <= '1';
                        bit_counter <= 1;
                    end if;
                end if;
            else
                clk_div <= clk_div + 1;
                data_valid <= '0';
            end if;
        end if;
    end process;
end Behavioral;

这个VHDL代码实现了一个简单的RS422接收模块，假设系统时钟频率为100 MHz，并且目标波特率为9600。代码包括以下几个部分：

1. 端口声明：定义输入和输出端口，包括系统时钟、复位信号、RS422输入信号、数据输出和数据有效信号。
2. 内部信号和常量：定义内部信号和常量，包括位计数器、移位寄存器、接收标志和时钟分频器。
3. 主进程：在时钟上升沿和复位信号的控制下，执行接收逻��。包括检测起始位、移位数据位和检测停止位。

请根据你的具体需求和硬件环境调整代码中的常量和参数。