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摘要

文章为学习记录。采用时序逻辑和组合逻辑实现边沿检测的核心逻辑。组合逻辑实现的上升沿和下降沿的脉冲比时序逻辑实现的上升沿和下降沿的脉冲提前一拍。

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一、边沿检测

边沿检测主要作用是能够准确的识别出单比特信号的上升沿或下降沿。
边沿检测原理：利用寄存器对信号前一状态和后一状态进行寄存，若前后两个状态不同，则检测到了边沿。

二、时序逻辑实现

仿真波形如下图所示。

2.1 rtl

module edge_dect(
input  wire  clk,
input  wire  rst_n,
input  wire  data,

output reg   pos_edge,
output reg   neg_edge
    );

reg  data_reg1;
reg  data_reg2;
reg  data_reg3;

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        begin
            data_reg1 <= 0;
            data_reg2 <= 0;
            data_reg3 <= 0;
        end
    else
        begin
            data_reg1 <= data;
            data_reg2 <= data_reg1;
            data_reg3 <= data_reg2;
        end
end

always @(posedge clk or negedge rst_n)
begin
    if(rst_n == 1'b0)
       pos_edge <= 1'b0;
    else if(data_reg2 && (~data_reg3)) 
       pos_edge <= 1'b1;
   else 
       pos_edge <= 1'b0;
end


always @(posedge clk or negedge rst_n)
begin
    if(rst_n == 1'b0)
       neg_edge <= 1'b0;
    else if((~data_reg2) && data_reg3) 
       neg_edge <= 1'b1;
   else 
       neg_edge <= 1'b0;
end

endmodule

2.2 tb

module tb_edge_dect();

reg  clk;
reg  rst_n;
reg  data;

wire   pos_edge;
wire   neg_edge;

initial
begin
    rst_n = 0;
    data  = 0;
    #101;
    rst_n = 1;
    #200;
    data  = 1;
    #500;
    data  = 0;
    #200;
    $stop;
end


initial
begin
    clk = 1;
end
always #10 clk = ~clk;

edge_dect  edge_dect_inst1
(
. clk(clk),
. rst_n(rst_n),
. data(data),

. pos_edge(pos_edge),
. neg_edge(neg_edge)
    );

endmodule

三、组合逻辑实现

仿真波形如下图所示。

3.1 rtl

module edge_dect(
input  wire  clk,
input  wire  rst_n,
input  wire  data,

output wire   pos_edge,
output wire   neg_edge
    );

reg  data_reg1;
reg  data_reg2;
reg  data_reg3;

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        begin
            data_reg1 <= 0;
            data_reg2 <= 0;
            data_reg3 <= 0;
        end
    else
        begin
            data_reg1 <= data;
            data_reg2 <= data_reg1;
            data_reg3 <= data_reg2;
        end
end

assign pos_edge = data_reg2 && (~data_reg3);
assign neg_edge = ~data_reg2 && data_reg3;
//always @(posedge clk or negedge rst_n)
//begin
//    if(rst_n == 1'b0)
//       pos_edge <= 1'b0;
//    else if(data_reg2 && (~data_reg3)) 
//       pos_edge <= 1'b1;
//   else 
//       pos_edge <= 1'b0;
//end


//always @(posedge clk or negedge rst_n)
//begin
//    if(rst_n == 1'b0)
//       neg_edge <= 1'b0;
//    else if((~data_reg2) && data_reg3) 
//       neg_edge <= 1'b1;
//   else 
//       neg_edge <= 1'b0;
//end

endmodule

3.2 tb

tb文件与时序逻辑实现的tb文件一样。