FPGA 串口

﹏ヽ暗。殇╰゛Y 2022-12-21 10:58 158阅读 0赞

第一：基本知识

波特率：描述的是一秒钟设备接受或者发送的码元个数，由于调制方式不同，因此一个码元可能包含多个比特或者一个比特。因此波特率并不代表串口发送或者接收数据的速率。

比特率：每秒钟传送的二进制位数，单位b/s,bit/s .

严格来说，波特率不在传输领域，出现传输、信道等字眼容易产生混淆，波特率描述的是单位时间内调制信号的能力，经它调制出来的信号才以比特的形式来传输，或者这样说，信号在传输过程中，如果要经过数模转换，就需要调制，那么传输时间除了消耗在其它领域外，还消耗在调制过程和在信道的传输过程，描述信号调制能力用波特率，描述信号传输能力用比特率。波特率与比特率的关系也可换算成：比特率=波特率\*单个调制状态对应的二进制位数。

晶体分为有缘晶振（oscillator，震荡器）和 无源晶振（crystal）

第二： FPGA 的串口USB 之间的硬件电路

FPGA 通过串口与上位机间的通信，FPGA 采用的是串口，PC端 采用的是 USB ，因此需要串口转USB ，FPGA逻辑电平3.3 V 代表1，0V 代表0.

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第三： FPGA 串口间的源程序和仿真

module uart_byte_tx(
        Clk,
        Reset_n,
        Data,
        Send_en,
        Baud_set,
        uart_tx,
        Tx_done
    );
        input Clk;
        input Reset_n;
        input [7:0]Data;
        input Send_en;
        input [2:0]Baud_set;
        output reg uart_tx;
        output reg Tx_done;
        
        //Baud_set = 0   就让波特率 = 9600；
        //Baud_set = 1   就让波特率 = 19200
        //Baud_set = 2   就让波特率 = 38400；
        //Baud_set = 3   就让波特率 = 57600；   
        //Baud_set = 4   就让波特率 = 115200； 
    
        reg [17:0]bps_DR;
        always@(*)
            case(Baud_set)
                0:bps_DR = 1000000000/9600/20;
                1:bps_DR = 1000000000/19200/20;
                2:bps_DR = 1000000000/38400/20;
                3:bps_DR = 1000000000/57600/20;
                4:bps_DR = 1000000000/115200/20;
                default:bps_DR = 1000000000/9600/20;
             endcase
    
        wire bps_clk;
        assign bps_clk = (div_cnt == 1);
        
        reg [17:0]div_cnt;
        always@(posedge Clk or negedge Reset_n)
        if(!Reset_n)
            div_cnt <= 0;
        else if(Send_en)begin
            if(div_cnt == bps_DR - 1)
                div_cnt <= 0;
            else 
                div_cnt <= div_cnt + 1'b1;
        end
        else
            div_cnt <= 0;
    
        reg [3:0]bps_cnt;
        always@(posedge Clk or negedge Reset_n)
        if(!Reset_n)
            bps_cnt <= 0;
        else if(Send_en)begin
           // if(bps_clk)begin
    	   if(div_cnt == 1)begin
                if(bps_cnt == 11)
                    bps_cnt <= 0;
                else
                    bps_cnt <= bps_cnt + 1'b1;
            end
        end
        else
            bps_cnt <= 0;
        
        always@(posedge Clk or negedge Reset_n)
        if(!Reset_n) begin
            uart_tx <= 1'b1;
            Tx_done <= 0;
        end
        else begin
            case(bps_cnt)
                1:begin uart_tx <= 0;Tx_done <= 1'b0;end
                2:uart_tx <= Data[0];
                3:uart_tx <= Data[1];
                4:uart_tx <= Data[2];
                5:uart_tx <= Data[3];
                6:uart_tx <= Data[4];
                7:uart_tx <= Data[5];
                8:uart_tx <= Data[6];
                9:uart_tx <= Data[7]; 
                10:uart_tx <= 1;
                11:begin uart_tx <= 1;Tx_done <= 1'b1;end
                default:uart_tx <= 1;
            endcase
         end     
    
    endmodule

仿真代码：

`timescale 1ns / 1ps
    
    module uart_byte_tx_tb();
        
        reg Clk;
        reg Reset_n;
        reg [7:0]Data;
        reg Send_en;
        reg [2:0]Baud_set;
        wire uart_tx;
        wire Tx_done; 
        
        uart_byte_tx uart_byte_tx(
            .Clk(Clk),
            .Reset_n(Reset_n),
            .Data(Data),
            .Send_en(Send_en),
            .Baud_set(Baud_set),
            .uart_tx(uart_tx),
            .Tx_done(Tx_done)
        );
        
        initial Clk = 1;
        always#10 Clk = ~Clk;
        
        initial begin
            Reset_n = 0;
            Data = 0;
            Send_en = 0;
            Baud_set = 4;
            #201;
            Reset_n = 1;
            #100;
            Data = 8'h57;
            Send_en = 1;
            #20;
            @(posedge Tx_done);
            Send_en = 0;
            #20000;
            Data = 8'h75;
            Send_en = 1;
            #20;
            @(posedge Tx_done);
            #20000;
            Send_en = 0;
            $stop;
        end
        
    endmodule

，

参考文献：[电子元件:无源晶振与有源晶振][Link 1]

[一文教你区分有源晶振与无源晶振][Link 2]

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[Link 1]: https://bbs.elecfans.com/jishu_299377_1_1.html
[Link 2]: http://murata.eetrend.com/article/2020-07/1003665.html#:~:text=%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E5%92%8C%E6%97%A0%E6%BA%90%E6%99%B6%E6%8C%AF%E7%9A%84%E5%8C%BA%E5%88%AB.%201%E3%80%81%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E6%AF%94%E8%BE%83%E8%B4%B5%EF%BC%8C%E4%BD%86%E6%98%AF%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E8%87%AA%E8%BA%AB%E5%B0%B1%E8%83%BD%E9%9C%87%E5%8A%A8%E3%80%82.%20%E8%80%8C%E6%97%A0%E8%AE%BA%E6%98%AF%E6%97%A0%E6%BA%90%E6%99%B6%E6%8C%AF%EF%BC%8C%E8%BF%98%E6%98%AF%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%EF%BC%8C%E9%83%BD%E6%9C%89%E8%87%AA%E8%BA%AB%E7%9A%84%E4%BC%98%E7%82%B9%E5%92%8C%E7%BC%BA%E7%82%B9%E6%89%80%E5%9C%A8%EF%BC%8C%E8%8B%A5%E8%80%83%E8%99%91%E4%BA%A7%E5%93%81%E6%88%90%E6%9C%AC%EF%BC%8C%E5%BB%BA%E8%AE%AE%E5%8F%AF%E4%BB%A5%E9%80%89%E6%8B%A9%E6%97%A0%E6%BA%90%E6%99%B6%E6%8C%AF%E7%94%B5%E8%B7%AF%EF%BC%9B%E8%8B%A5%E8%80%83%E8%99%91%E4%BA%A7%E5%93%81%E6%80%A7%E8%83%BD%EF%BC%8C%E5%BB%BA%E8%AE%AE%E9%80%89%E6%8B%A9%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E7%94%B5%E8%B7%AF%EF%BC%8C%E7%9C%81%E6%97%B6%E6%96%B9%E4%BE%BF%E4%B9%9F%E8%83%BD%E4%BF%9D%E8%AF%81%E4%BA%A7%E5%93%81%E6%80%A7%E8%83%BD%E3%80%82.%202%E3%80%81%E6%97%A0%E6%BA%90%E6%99%B6%E6%8C%AF%E6%9C%80%E9%AB%98%E7%B2%BE%E5%BA%A6%E4%B8%BA5ppm%EF%BC%8C%E8%80%8C%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E7%9A%84%E7%B2%BE%E5%BA%A6%E5%88%99%E5%8F%AF%E4%BB%A5%E8%BE%BE%E5%88%B00.1ppm%E3%80%82.,%E7%B2%BE%E5%BA%A6%E8%B6%8A%E9%AB%98%EF%BC%8C%E9%A2%91%E7%8E%87%E7%A8%B3%E5%AE%9A%E6%80%A7%E4%B9%9F%E6%9B%B4%E5%A5%BD%E3%80%82.%20%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E5%9C%A8%E7%A8%B3%E5%AE%9A%E6%80%A7%E4%B8%8A%E8%A6%81%E8%83%9C%E8%BF%87%E6%97%A0%E6%BA%90%E6%99%B6%E6%8C%AF%EF%BC%8C%E4%BD%86%E4%B9%9F%E6%9C%89%E8%87%AA%E8%BA%AB%E5%B0%8F%E5%B0%8F%E7%9A%84%E7%BC%BA%E9%99%B7%EF%BC%8C%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E7%9A%84%E4%BF%A1%E5%8F%B7%E7%94%B5%E5%B9%B3%E6%98%AF%E5%9B%BA%E5%AE%9A%EF%BC%8C%E6%89%80%E4%BB%A5%E9%9C%80%E8%A6%81%E9%80%89%E6%8B%A9%E5%A5%BD%E5%90%88%E9%80%82%E8%BE%93%E5%87%BA%E7%94%B5%E5%B9%B3%EF%BC%8C%E7%81%B5%E6%B4%BB%E6%80%A7%E8%BE%83%E5%B7%AE%E3%80%82.%203%E3%80%81%E6%9C%89%E6%BA%90%E6%99%B6%E6%8C%AF%E4%B8%80%E8%88%AC4%E4%B8%AA%E8%84%9A%EF%BC%8C%E4%B8%80%E4%B8%AA%E7%94%B5%E6%BA%90%EF%BC%8C%E4%B8%80%E4%B8%AA%E6%8E%A5%E5%9C%B0%EF%BC%8C%E4%B8%80%E4%B8%AA%E4%BF%A1%E5%8F%B7%E8%BE%93%E5%87%BA%E7%AB%AF%EF%BC%8C%E4%B8%80%E4%B8%AANC%EF%BC%88%E7%A9%BA%E8%84%9A%EF%BC%89%E3%80%82.%20%E6%9C%89%E4%B8%AA%E7%82%B9%E6%A0%87%E8%AE%B0%E7%9A%84%E4%B8%BA1%E8%84%9A%EF%BC%8C%E6%8C%89%E9%80%86%E6%97%B6%E9%92%88%EF%BC%88%E7%AE%A1%E8%84%9A%E5%90%91%E4%B8%8B%EF%BC%89%E5%88%86%E5%88%AB%E4%B8%BA2%E3%80%813%E3%80%814%E3%80%82.