串口通信，fpga怎么写代码

FPGA串口通信的实现需要创建一个串口模块。下面是一个例子，实现了一个简单的串口通信：

module uart(
  input clk,
  input resetn,
  input tx_start,
  input [7:0] tx_data,
  output tx_busy,
  output reg tx_done,
  input rx_start,
  output [7:0] rx_data,
  output reg rx_done
);

// 定义波特率
parameter BAUD_RATE = 9600;
// 计算波特率分频系数
parameter DIVISOR = $floor(50000000/BAUD_RATE);

// 定义状态机状态
parameter [1:0] IDLE = 2'b00, START = 2'b01, DATA = 2'b10, STOP = 2'b11;

// 定义状态机信号
reg [1:0] state = IDLE;
reg [3:0] count;

// 定义发送和接收数据寄存器
reg [7:0] tx_reg, rx_reg;

// 定义发送和接收完成标志
reg tx_complete, rx_complete;

// 定义发送和接收忙碌标志
assign tx_busy = tx_complete ? 1'b0 : 1'b1;

// 定义时钟分频计数器
reg [15:0] divider = 0;

// 时钟分频
always @(posedge clk) begin
  if (!resetn) begin
    divider <= 0;
  end else begin
    divider <= divider + 1;
  end
end

// 发送状态机
always @(posedge clk) begin
  if (!resetn) begin
    state <= IDLE;
    count <= 4;
    tx_done <= 1'b0;
  end else begin
    case (state)
      IDLE: begin
        if (tx_start) begin
          tx_reg <= tx_data;
          state <= START;
          count <= 0;
          tx_complete <= 0;
        end
      end
      START: begin
        if (count < DIVISOR) begin
          count <= count + 1;
        end else begin
          count <= 0;
          state <= DATA;
        end
      end
      DATA: begin
        if (count < 8) begin
          tx_reg <= {tx_reg[6:0], 1'b0};
          count <= count + 1;
        end else begin
          count <= 0;
          state <= STOP;
        end
      end
      STOP: begin
        if (count < DIVISOR) begin
          count <= count + 1;
        end else begin
          count <= 0;
          state <= IDLE;
          tx_complete <= 1'b1;
          tx_done <= 1'b1;
        end
      end
    endcase
  end
end

// 接收状态机
always @(posedge clk) begin
  if (!resetn) begin
    state <= IDLE;
    count <= 0;
    rx_done <= 1'b0;
    rx_complete <= 0;
  end else begin
    case (state)
      IDLE: begin
        if (rx_start) begin
          state <= START;
          count <= 0;
        end
      end
      START: begin
        if (count < DIVISOR/2) begin
          count <= count + 1;
        end else begin
          count <= 0;
          state <= DATA;
        end
      end
      DATA: begin
        if (count < 8) begin
          rx_reg <= {rx_reg[6:0], rx_start};
          count <= count + 1;
        end else begin
          count <= 0;
          state <= STOP;
        end
      end
      STOP: begin
        if (count < DIVISOR/2) begin
          count <= count + 1;
        end else begin
          count <= 0;
          state <= IDLE;
          rx_complete <= 1'b1;
          rx_done <= 1'b1;
        end
      end
    endcase
  end
end

// 输出接收数据
assign rx_data = rx_reg;

endmodule

在上面的例子中，我们通过定义一个带有时钟和复位输入的 `uart` 模块来实现串口通信。其中，模块包括了发送和接收状态机、发送和接收数据寄存器以及时钟分频计数器。通过调整波特率和分频系数，可以实现不同的串口通信速率。