Description:

Create a set of counters suitable for use as a 12-hour clock (with am/pm indicator). Your counters are clocked by a fast-runningclk, with a pulse onenawhenever your clock should increment (i.e., once per second).

resetresets the clock to 12:00 AM.pmis 0 for AM and 1 for PM.hh,mm, andssare twoBCD

The following timing diagram shows the rollover behaviour from11:59:59 AMto12:00:00 PMand the synchronous reset and enable behaviour.

module top_module(
    input clk,
    input reset,
    input ena,
    output pm,
    output [
 
7:0] hh,
    output [7:0] mm,
    output [7:0] ss);     
    always@(posedge clk)begin
        if(reset|(ena&&ss[7:0]==8'h59))
             ss<=8'h00;
        else begin
           if(ena&&ss[3:0]==4'h9)
               ss[3:0]<=0;
           else begin
             if(ena)
               ss[
 
3:0]<=ss[3:0]+1;
             else
               ss[3:0]<=ss[3:0];
           end
            
           if(ena&&ss[3:0]==4'h9)
            ss[7:4]<=ss[7:4]+1;
           else
            ss[7:4]<=ss[7:4];
        end
    end
    //秒
    always@(posedge clk)begin
        if(reset|(ena&&mm==8'h59&&ss==8'h59))
            mm[7:0]<=8'h00;
        else begin
              if(ena&&ss[7:0]==8'h59)
                 mm[3:0]<=mm[3:0]+1;
              if(ena&&mm[3:0]==4'h9&&ss[7:0]==8'h59)begin
                 mm[7:4]<=mm[7:4]+1;
                 mm[3:0]<=0;
              end
            end
    end
    //分鐘
   always@(posedge clk)begin
       if(reset)begin
           hh[7:0]<=8'h12;
           pm<=0;
       end
       else begin
           if(ena&&hh[7:0]==8'h11&&mm[7:0]==8'h59&&ss[7:0]==8'h59)begin
                pm<=~pm;
                hh[7:0]<=8'h12;
           end
           if(ena&&ss[7:0]==8'h59&&mm[7:0]==8'h59)begin
               if(hh[7:0]==8'h12)
                    hh[7:0]<=8'h01;
               else
                   if(hh[3:0]==4'h9)begin
                       hh[7:4]<=hh[7:4]+1;
                hh[3:0]<=4'h00;
                   end
               else
                   hh[3:0]<=hh[3:0]+1;  
           end
           
       end
   
    end

        

endmodule
        

（初學Verilog，如果有大佬看見歡迎指教)