write a uart module use fpga verilog

Sure, I can help you with that!

Here is an example code for a UART module written in Verilog for an FPGA:

module uart (
    input clk,
    input reset,
    input uart_rx,
    output uart_tx
);

    // baud rate parameters
    parameter BAUD_RATE = 9600;
    parameter CLK_FREQ = 100000000;

    // internal registers
    reg [7:0] tx_data;
    reg [7:0] rx_data;
    reg [3:0] tx_bit_count;
    reg [3:0] rx_bit_count;
    reg tx_busy;
    reg rx_busy;
    reg tx_enable;
    reg rx_enable;
    reg rx_start;

    // calculate divisor for specified baud rate
    localparam DIVISOR = CLK_FREQ / (BAUD_RATE * 16);

    // clock divider for baud rate
    reg [15:0] clk_div;
    always @(posedge clk) begin
        if (reset) begin
            clk_div <= 0;
        end else begin
            clk_div <= clk_div + 1;
        end
    end

    // tx state machine
    reg [1:0] tx_state;
    localparam TX_IDLE = 2'b00;
    localparam TX_START = 2'b01;
    localparam TX_DATA = 2'b10;
    localparam TX_STOP = 2'b11;
    always @(posedge clk) begin
        if (reset) begin
            tx_state <= TX_IDLE;
            tx_bit_count <= 0;
            tx_busy <= 0;
        end else begin
            case (tx_state)
                TX_IDLE:
                    if (tx_enable) begin
                        tx_state <= TX_START;
                        tx_busy <= 1;
                    end
                TX_START:
                    if (clk_div == DIVISOR) begin
                        uart_tx <= 0;
                        tx_data <= 8'b00000001;
                        tx_bit_count <= 0;
                        tx_state <= TX_DATA;
                    end
                TX_DATA:
                    if (clk_div == DIVISOR) begin
                        uart_tx <= tx_data[tx_bit_count];
                        tx_bit_count <= tx_bit_count + 1;
                        if (tx_bit_count == 8) begin
                            tx_state <= TX_STOP;
                        end
                    end
                TX_STOP:
                    if (clk_div == DIVISOR) begin
                        uart_tx <= 1;
                        tx_state <= TX_IDLE;
                        tx_busy <= 0;
                    end
            endcase
        end
    end

    // rx state machine
    reg [1:0] rx_state;
    localparam RX_IDLE = 2'b00;
    localparam RX_START = 2'b01;
    localparam RX_DATA = 2'b10;
    localparam RX_STOP = 2'b11;
    always @(posedge clk) begin
        if (reset) begin
            rx_state <= RX_IDLE;
            rx_bit_count <= 0;
            rx_busy <= 0;
            rx_start <= 0;
        end else begin
            case (rx_state)
                RX_IDLE:
                    if (rx_enable && uart_rx == 0) begin
                        rx_state <= RX_START;
                        rx_busy <= 1;
                    end
                RX_START:
                    if (clk_div == DIVISOR) begin
                        rx_start <= 1;
                        rx_bit_count <= 0;
                        rx_data <= 0;
                        rx_state <= RX_DATA;
                    end
                RX_DATA:
                    if (clk_div == DIVISOR) begin
                        rx_data <= {rx_data[6:0], uart_rx};
                        rx_bit_count <= rx_bit_count + 1;
                        if (rx_bit_count == 7) begin
                            rx_state <= RX_STOP;
                        end
                    end
                RX_STOP:
                    if (clk_div == DIVISOR) begin
                        rx_start <= 0;
                        rx_busy <= 0;
                        rx_state <= RX_IDLE;
                    end
            endcase
        end
    end

endmodule

This code implements a simple UART module that can transmit and receive data at a specified baud rate. It uses a state machine to handle the transmit and receive operations, and a clock divider to generate the appropriate baud rate. The module has inputs for the system clock, reset signal, and UART receive signal, and an output for the UART transmit signal.

I hope this helps! Let me know if you have any questions.