编写uart串口通信的verilog代码

A：以下是一个简单的verilog代码示例，用于实现UART串口通信：

module uart_tx_rx (
   input clk,
   input rst_n,
   input [7:0] data_in,
   output tx_out,
   input rx_in
);

// 参数定义
parameter BAUD_RATE = 9600;
parameter COUNTER_MAX = $floor((1.0 / BAUD_RATE) * 100000000); // 单位为100MHz

// 状态定义
localparam IDLE = 2'd0;
localparam START = 2'd1;
localparam DATA = 2'd2;
localparam STOP = 2'd3;

// 寄存器定义
reg [2:0] state = IDLE;
reg [7:0] shift_reg;
reg [14:0] counter;

assign tx_out = (state != IDLE) ? shift_reg[0] : 1'b1;

// 主逻辑
always @(posedge clk or negedge rst_n) begin
   if (~rst_n) begin
      counter <= 0;
      shift_reg <= 8'h00;
      state <= IDLE;
   end else begin
      counter <= (counter == COUNTER_MAX - 1) ? 0 : counter + 1;
   
      case (state)
         IDLE: begin
            shift_reg <= 8'h00;
            if (~rx_in) begin
               state <= START;
               counter <= 0;
            end
         end
         
         START: begin
            if (counter == COUNTER_MAX - 1) begin
               state <= DATA;
               shift_reg <= {1'b0, data_in};
               counter <= 0;
            end
         end
         
         DATA: begin
            if (counter == COUNTER_MAX - 1) begin
               shift_reg <= {shift_reg[0], shift_reg[8:1]};
               counter <= 0;
               state <= (shift_reg == 8'h00) ? STOP : DATA;
            end
         end
         
         STOP: begin
            state <= IDLE;
         end
      endcase
   end
end

endmodule

此代码可以实现一个简单的UART串口通信。它将一个8位数据（data_in）通过串口发送出去，使用9600波特率进行通信。从串口接收的数据（rx_in）可以被忽略，该代码仅支持单向通信。