之前探讨过PS/2键盘编解码以及数据传输协议，这次自己动手实现了利用FPGA接收键盘编码，然后通过串口传输到PC。做的比较简单，只是通过FPGA把大写字母A-Z转换成相应的ASCII码，只要字母按键被按下，就能在串口调试助手里显示相应大写字母。下面就共享代码吧！
    除了顶层模块，三个底层模块分别为PS/2传输处理模块、串口传输模块以及串口波特率选择模块（下面只给出顶层模块和PS/2传输处理模块的verilog代码）。
module ps2_key(clk,rst_n,ps2k_clk,ps2k_data,rs232_tx);
input clk; //50M时钟信号
input rst_n;  //复位信号
input ps2k_clk;   //PS2接口时钟信号
input ps2k_data;  //PS2接口数据信号
output rs232_tx;  // RS232发送数据信号
wire[7:0] ps2_byte;  // 1byte键值
wire ps2_state;      //按键状态标志位
wire bps_start;   //接收到数据后，波特率时钟启动信号置位
wire clk_bps; // clk_bps的高电平为接收或者发送数据位的中间采样点
ps2scan           ps2scan(   .clk(clk),            //按键扫描模块
                            .rst_n(rst_n),             
                            .ps2k_clk(ps2k_clk),
                            .ps2k_data(ps2k_data),
                             .ps2_byte(ps2_byte),
                            .ps2_state(ps2_state)
                            );
speed_select  speed_select( .clk(clk),
                                   .rst_n(rst_n),
                                   .bps_start(bps_start),
                                   .clk_bps(clk_bps)
                                   );
my_uart_tx    my_uart_tx(       .clk(clk),
                                   .rst_n(rst_n),
                                   .clk_bps(clk_bps),
                                   .rx_data(ps2_byte),
                                   .rx_int(ps2_state),
                                   .rs232_tx(rs232_tx),
                                   .bps_start(bps_start)
                                   );
Endmodule
module ps2scan(clk,rst_n,ps2k_clk,ps2k_data,ps2_byte,ps2_state);
input clk; //50M时钟信号
input rst_n;  //复位信号
input ps2k_clk;   //PS2接口时钟信号
input ps2k_data;  //PS2接口数据信号
output[7:0] ps2_byte;    // 1byte键值，只做简单的按键扫描
output ps2_state;    //键盘当前状态，ps2_state=1表示有键被按下
//------------------------------------------
reg ps2k_clk_r0,ps2k_clk_r1,ps2k_clk_r2;  //ps2k_clk状态寄存器
//wire pos_ps2k_clk;     // ps2k_clk上升沿标志位
wire neg_ps2k_clk;   // ps2k_clk下降沿标志位
always @ (posedge clk or negedge rst_n) begin
    if(!rst_n) begin
           ps2k_clk_r0 <= 1'b0;
           ps2k_clk_r1 <= 1'b0;
           ps2k_clk_r2 <= 1'b0;
       end
    else begin                         //锁存状态，进行滤波
           ps2k_clk_r0 <= ps2k_clk;
           ps2k_clk_r1 <= ps2k_clk_r0;
           ps2k_clk_r2 <= ps2k_clk_r1;
       end
end
assign neg_ps2k_clk = ~ps2k_clk_r1 & ps2k_clk_r2;    //下降沿
//------------------------------------------
reg[7:0] ps2_byte_r;     //PC接收来自PS2的一个字节数据存储器
reg[7:0] temp_data;  //当前接收数据寄存器
reg[3:0] num; //计数寄存器
always @ (posedge clk or negedge rst_n) begin
    if(!rst_n) begin
           num <= 4'd0;
           temp_data <= 8'd0;
       end
    else if(neg_ps2k_clk) begin //检测到ps2k_clk的下降沿
           case (num)
              4'd0:  num <= num+1'b1;
              4'd1:  begin
                         num <= num+1'b1;
                         temp_data[0] <= ps2k_data;  //bit0
                     end
              4'd2:  begin
                         num <= num+1'b1;
                         temp_data[1] <= ps2k_data;  //bit1
                     end
              4'd3:  begin
                         num <= num+1'b1;
                         temp_data[2] <= ps2k_data;  //bit2
                     end
              4'd4:  begin
                         num <= num+1'b1;
                         temp_data[3] <= ps2k_data;  //bit3
                     end
              4'd5:  begin
                         num <= num+1'b1;
                         temp_data[4] <= ps2k_data;  //bit4
                     end
              4'd6:  begin
                         num <= num+1'b1;
                         temp_data[5] <= ps2k_data;  //bit5
                     end
              4'd7:  begin
                         num <= num+1'b1;
                         temp_data[6] <= ps2k_data;  //bit6
                     end

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