module M10_counter(
    input EN,   //使能端
    input CP, //时钟
    input Rd, //清零
    output reg Cout, //进位
    output reg [3:0] Q //输出
    );

always @ (posedge CP,negedge Rd)
if(~Rd) Q<=4'b0000;  //异步清零
else if(EN) begin
    if(Q<4'b1001) Q<=Q+1'b1; //加计数
    else Q<=4'b0000;
end
else Q<=Q;
   always @ (Q)
    if(Q==4'b1001) Cout =1; //进位
    else Cout=0;

endmodule

module M10_counter_tb();
    reg EN,CP,Rd;
    wire Cout;
    wire [3:0] Q;
    M10_counter test(.EN(EN),
                     .CP(CP),
                     .Rd(Rd),
                     .Cout(Cout),
                     .Q(Q)  );
        initial fork
            CP=0;
            EN=1; #20 EN=0; #50 EN=1;
            Rd=0; #30 Rd=1;
           join
           always #8 CP=~CP;
endmodule