//Author:"泪与汗的缠绵"

//Data：2011-11月

//功能：数电器件74系列之优先级编码器----74HC148

其归纳如下：

http://s14/middle/7dc6e9754b254eafead7d&690

module Makecode(indata,outcode,EI,GS,E0);
       input [7:0] indata;//数据输入端
       input EI;
       output [2:0]outcode;
       output GS,E0;
       reg  [2:0]outcode;
       reg  GS,E0;
   always@(negedge indata  or posedge EI)
 begin
  if(EI)
     begin
    outcode<=3'b111;
    GS<=1'b1;
    E0<=1'b1;
     end
  else
    begin
    casex(indata)
      8'b1111_1111:
        begin
          outcode<=3'b111;
          GS<=1'b1;
          E0<=1'b0;
        end
      8'b1xxx_xxxx:
        begin
          outcode<=3'b000;
          GS<=1'b0;
          E0<=1'b1;
        end
      8'bx1xx_xxx:
        begin
          outcode<=3'b001;
          GS<=1'b0;
          E0<=1'b1;
        end
      8'bxx1x_xxxx:
        begin
          outcode<=3'b010;
          GS<=1'b0;
          E0<=1'b1;
           end
      8'bxxx1_xxxx:
        begin
          outcode<=3'b011;
          GS<=1'b0;
          E0<=1'b1;
        end
      
      8'bxxxx_1xxx:
        begin
          outcode<=3'b100;
          GS<=1'b0;
          E0<=1'b1;
        end
      8'bxxxx_x1xx:
        begin
          outcode<=3'b101;
          GS<=1'b0;
          E0<=1'b1;
        end
      8'bxxxx_xx1x:
        begin
          outcode<=3'b110;
          GS<=1'b0;
          E0<=1'b1;
        end
      8'bxxxx_xxx1:
        begin
          outcode<=3'b111;
          GS<=1'b0;
          E0<=1'b1;
        end
     default:outcode<=3'bxxx; 
    endcase
    end
    end
endmodule