mokcounter.v

ＦＰＧＡ实现全数字锁相环

module moKcounter(//input                                             
                   clk,se,K,reset,                                    
                   //output                                           
                    carry,borrow);                        
 input se,clk,reset;                                                  
 input[3:0] K;                                                        
 reg[16:0] kmode,count;                                            
 output carry,borrow;                                             
                                          
 wire  carry,borrow;                                           
 always @(K)                                                          
 begin                                                                
  case(K)                                                             
4'd1:kmode=17'd7;        
4'd2:kmode=17'd15;       
4'd3:kmode=17'd31;       
4'd4:kmode=17'd63;       
4'd5:kmode=17'd127;      
4'd6:kmode=17'd255;      
4'd7:kmode=17'd511;      
4'd8:kmode=17'd1023;     
4'd9:kmode=17'd2047;     
4'd10:kmode=17'd4096;    
4'd11:kmode=17'd8191;    
4'd12:kmode=17'd16383;   
4'd13:kmode=17'd32767;   
4'd14:kmode=17'd65535;
4'd15:kmode=17'd131071;
default:kmode=17'bz;                                           
  endcase                                                             
  end
                                                                 
 always @(posedge clk or reset)                                                
 begin                                                                
 if(!reset)  count=0;                                
 else if(se) begin if(count==0) count=kmode[16:1];  
                   else  count=count-1;                
             end                                                      
 else begin if(count==kmode)  count=kmode[16:1];     
            else count=count+1;                                     
      end                                                             
 end
 assign carry=(count>=kmode-7)&&(~se);
 assign borrow=(count<=7)&&se;                                                                  
 endmodule