P6-13 非方塊程序指定 4-bit register

//KEY[0] PIN_G26  ==> CLK
//KEY[1] PIN_N23  ==> RES
//KEY[2] PIN_P23
//SW[0]    PIN_N25  ==> Din 
// LEDG[0] PIN_AE22 ==> Qout[0]
// LEDG[1] PIN_AF22 ==> Qout[1]
// LEDG[2] PIN_W19  ==> Qout[2]
// LEDG[3] PIN_V18  ==> Qout[3]




//--------------------------------------------------
//4-bit register for Non-blocking Procedural Assignment
//Filename : reg_nbp.v
//--------------------------------------------------
module reg4_nbp(Qout, CLK, RESET, Din);
output [3:0] Qout;
input CLK, RESET;
input Din;

reg [3:0] Qout;


always @ (posedge CLK or negedge RESET)
//Positive edge CLK and asynchronous RESET
 if (!RESET)
   Qout <= 4'b0000;
 else
  begin
   Qout[0] <= Din;
   Qout[1] <= Qout[0];
   Qout[2] <= Qout[1];
   Qout[3] <= Qout[2];
  end
endmodule