按键消抖（用状态机实现）

基于状态机的设计代码 

module key_filter(
    clk,
    rst,
    key,
    key_p_flag,
    key_r_flag,
    key_state
    );
    
    input clk,rst;
    input key;
    output reg key_p_flag;
    output reg key_r_flag;
    output reg key_state;
     
    reg [1:0]r_key;        //后面用来判断什么时候pedge，什么时候nedge
    always@(posedge clk)
        r_key<={r_key[0],key};   //位拼接
        
    wire pedge_key;
    assign pedge_key=r_key==2'b01;   //识别到key的上升沿
    wire nedge_key;
    assign nedge_key=r_key==2'b10;  //识别到key的下降沿
     
    reg [19:0]cnt;
    localparam IDLE=0;
    
    reg [1:0]state;
    always@(posedge clk or negedge rst)
        if(!rst)begin
            state<=0;
            key_r_flag<=0;
            key_p_flag<=0;
            cnt<=0;
            key_state<=1;
        end
        else begin 
            case (state)
                0:
                    begin
                        key_r_flag<=0;
                        
                        if(nedge_key)
                            state<=1;
                        else
                            state<=0;
                    end
               1:
                    if((pedge_key)&&(cnt<1000000-1))
                        begin
                            cnt<=0;
                            state<=0;
                        end 
                    else if(cnt>=1000000-1)
                        begin             
                            state<=2;
                            cnt<=0;         //给计数器清零，为下一次计数做准备
                            key_p_flag<=1;
                            key_state<=0;
                        end
                    else 
                        begin
                            state<=1;
                            cnt<=cnt+1;
                        end                    
               2:
                    begin
                        key_p_flag<=0;
    
                        if(pedge_key)
                            state<=3;
                        else
                            state<=2;
                    end 

               3:
                    if((nedge_key)&&(cnt<1000000-1))
                        begin
                            state<=2;
                            state<=0;
                        end
                    else if(cnt>=1000000-1) 
                        begin
                        state<=0;
                        cnt<=0;         //给计数器清零，为下一次计数做准备
                        key_r_flag<=1;
                        key_state<=1;
                        end
                    else 
                        begin
                        state<=3;
                        cnt<=cnt+1;
                        end
           endcase
       end
    
endmodule

testbench代码 

`timescale 1ns / 1ps

module key_filter_tb();
    
    reg clk,rst;
    reg key;
    wire key_p_flag;
    wire key_r_flag;
    wire key_state;    
    
    key_filter key_filter(
        clk,
        rst,
        key,
        key_p_flag,
        key_r_flag,
        key_state
    );
    
    initial clk=1;
    always #10 clk=~clk;
    
    initial begin
        rst=0;
        key=1;
        #201;
        rst=1;
        #3000;
        
        key=0;
        #20000;     //20ns,模拟按键抖动
        key=1;
        #30000;     //30ns,模拟按键抖动
        key=0;
        #20000;     //20ns,模拟按键抖动
        key=1;
        #30000;     //30ns,模拟按键抖动
        key=0;
        #50000000;    //50ms
        
        key=1;
        #20000;     //20ns,模拟按键抖动
        key=0;
        #30000;     //30ns,模拟按键抖动
        key=1;
        #20000;     //20ns,模拟按键抖动
        key=0;
        #30000;     //30ns,模拟按键抖动
        key=1;
        #50000000;    //50ms        
        $stop;
    end
endmodule

 仿真验证波形

在按下抖动的过程中，key在抖动但是p_flag并没有出现高脉冲 ，直到稳定了20ms后p_flag出现了高脉冲。

 并只稳定了一个时钟周期后就变为0

R_flag也是同样

在输出端再加入一个key_state，模拟什么时候确定按键按下，什么时候按键释放