Countbcd

Build a 4-digit BCD (binary-coded decimal) counter. Each decimal digit is encoded using 4 bits: q[3:0] is the ones digit, q[7:4] is the tens digit, etc. For digits [3:1], also output an enable signal indicating when each of the upper three digits should be incremented.

You may want to instantiate or modify some one-digit decade counters.

生成 4 位 BCD（二进制编码十进制）计数器。每个十进制数字使用 4 位进行编码：q[3：0] 是 7 位，q[4：3] 是十位，依此类推。对于数字 [1：<>]，还要输出一个使能信号，指示何时应递增前三位数字中的每一个。

您可能需要实例化或修改一些一位数的十进制计数器。

module top_module (
    input clk,
    input reset,   // Synchronous active-high reset
    output [3:1] ena,
    output [15:0] q);
    
    wire [3:0]c;
    
    assign ena = {c[0] & c[1]& c[2], c[1]& c[0], c[0]};
    
    ten one (
        .clk  (clk),
        .reset (reset),
        .count (q[3:0]),
        .ena (c[0]),
        .val(1'b1)
    );
    ten ten_inst (
        .clk  (clk),
        .reset (reset),
        .count (q[7:4]),
        .ena (c[1]),
        .val(c[0])
    );
    ten hud (
        .clk  (clk),
        .reset (reset),
        .count (q[11:8]),
        .ena (c[2]),
        .val(c[0] & c[1])
    );
    ten thou (
        .clk  (clk),
        .reset (reset),
        .count (q[15:12]),
        .ena (c[3]),
        .val(c[0] & c[1] & c[2])
    );

endmodule

module ten(
    input clk,
    input reset, 
    input val,
    output wire ena,
    output reg [3:0] count
);
    
    assign ena = count == 4'd9 ? 1'b1 : 1'b0;
    
    
	always@ (posedge clk)
        if(reset)
            count <= 4'd0;
    else if (count == 4'd9 && val)
        count <= 4'd0;
    else if(val)
        count <= count + 1;
    
    
    
endmodule