题解 | #异步复位同步释放#

关于波形读有个问题： 如果同步释放代码这样写

    //异步复位,同步释放
    always @(posedge clk, negedge rst_n) begin
        if(!rst_n) begin
            rstn_reg <= 1'b0;
            rstn_reg_1 <= 1'b0;   
        end
        else begin
            rstn_reg <= 1'b1;
            rstn_reg_1 <= rstn_reg;  
        end
        
    end

在波形图 红色方框处是不是输出dout <= d 等于1 啊

所以同步释放应该这样写

    //异步复位,同步释放
    always @(posedge clk, negedge rst_n) begin
        if(!rst_n) begin
            rstn_reg <= 1'b0;
            rstn_reg_1 <= 1'b0;   
        end
        else begin
            rstn_reg <= rst_n;
            rstn_reg_1 <= rstn_reg;  
        end
        
    end

整体代码

`timescale 1ns/1ns

module ali16(
input clk,
input rst_n,
input d,
output reg dout
 );
    reg rstn_reg, rstn_reg_1;
    
    //异步复位,同步释放
    always @(posedge clk, negedge rst_n) begin
        if(!rst_n) begin
            rstn_reg <= 1'b0;
            rstn_reg_1 <= 1'b0;   
        end
        else begin
            rstn_reg <= rst_n;
            rstn_reg_1 <= rstn_reg;  
        end
        
    end
    
    //同步释放
//     always @(posedge clk) begin
//             rstn_reg_1 <= rstn_reg;       
//     end  
    
    //赋值
    always @(posedge clk, negedge rstn_reg_1) begin
        if(!rstn_reg_1) begin
            dout <= 1'b0;
        end
        else
            dout <= d;
        
    end    

//*************code***********//


//*************code***********//
endmodule