FPGA基于rs485的自环代码示例

以下是一个基于FPGA的RS485自环示例代码，供您参考：

module rs485_loopback (
    input wire CLK,
    input wire RESET,
    input wire RXDp,
    input wire RXDn,
    output wire TXDp,
    output wire TXDn
);

// 定义常量
parameter BAUD_RATE = 9600;
parameter HALF_BIT_TIME = 52083; // 时钟周期数

// 定义状态机状态
localparam IDLE = 2'b00;
localparam RECEIVE = 2'b01;
localparam TRANSMIT = 2'b10;

// 定义寄存器
reg [7:0] data_reg;
reg [7:0] tx_reg;
reg [7:0] rx_reg;
reg [1:0] state_reg;
reg [15:0] bit_count_reg;
reg [15:0] baud_count_reg;

// 定义时钟分频计数器
reg [3:0] clk_div_reg;

// 时钟分频，以获得所需的波特率
always @(posedge CLK) begin
    if (RESET == 1'b1) begin
        clk_div_reg <= 4'b0000;
    end else if (clk_div_reg == HALF_BIT_TIME - 1) begin
        clk_div_reg <= 4'b0000;
    end else begin
        clk_div_reg <= clk_div_reg + 1;
    end
end

// 状态机
always @(posedge CLK) begin
    if (RESET == 1'b1) begin
        state_reg <= IDLE;
    end else begin
        case (state_reg)
            IDLE: begin
                if (rx_reg[0] == 1'b1 && rx_reg[1] == 1'b0) begin
                    state_reg <= RECEIVE;
                    bit_count_reg <= 16;
                    baud_count_reg <= HALF_BIT_TIME;
                end else if (tx_reg != 8'h00) begin
                    state_reg <= TRANSMIT;
                    bit_count_reg <= 9;
                    baud_count_reg <= HALF_BIT_TIME;
                end else begin
                    state_reg <= IDLE;
                end
            end
            RECEIVE: begin
                if (baud_count_reg == HALF_BIT_TIME - 1) begin
                    if (bit_count_reg == 1) begin
                        rx_reg <= {1'b0, RXDp};
                        state_reg <= IDLE;
                    end else begin
                        rx_reg <= {rx_reg[1:0], RXDp};
                        bit_count_reg <= bit_count_reg - 1;
                    end
                    baud_count_reg <= 0;
                end else begin
                    baud_count_reg <= baud_count_reg + 1;
                end
            end
            TRANSMIT: begin
                if (baud_count_reg == HALF_BIT_TIME - 1) begin
                    if (bit_count_reg == 1) begin
                        tx_reg <= 8'h00;
                        state_reg <= IDLE;
                    end else begin
                        TXDp <= tx_reg[0];
                        tx_reg <= {tx_reg[6:0], 1'b0};
                        bit_count_reg <= bit_count_reg - 1;
                    end
                    baud_count_reg <= 0;
                end else begin
                    baud_count_reg <= baud_count_reg + 1;
                end
            end
        endcase
    end
end

// RS485收发数据
assign TXDn = 1'b1; // 驱动TXDn高电平，发送数据
assign TXDp = (state_reg == TRANSMIT && clk_div_reg == HALF_BIT_TIME / 2) ? tx_reg[0] : 1'b0; // 发送数据

assign rx_reg[0] = RXDn; // 接收数据
assign rx_reg[1] = RXDp;

endmodule

以上代码仅供参考，实际使用时需要根据具体的应用场景进行修改和调整。