题解 | #用优先编码器①实现键盘编码电路#

`timescale 1ns/1ns
module encoder_0(
   input      [8:0]         I_n   ,
   
   output reg [3:0]         Y_n   
);

always @(*)begin
   casex(I_n)
      9'b111111111 : Y_n = 4'b1111;
      9'b0xxxxxxxx : Y_n = 4'b0110;
      9'b10xxxxxxx : Y_n = 4'b0111;
      9'b110xxxxxx : Y_n = 4'b1000;
      9'b1110xxxxx : Y_n = 4'b1001;
      9'b11110xxxx : Y_n = 4'b1010;
      9'b111110xxx : Y_n = 4'b1011;
      9'b1111110xx : Y_n = 4'b1100;
      9'b11111110x : Y_n = 4'b1101;
      9'b111111110 : Y_n = 4'b1110;
      default      : Y_n = 4'b1111;
   endcase    
end 
     
endmodule

module key_encoder(
      input      [9:0]         S_n   ,         
 
      output wire[3:0]         L     ,
      output wire              GS
);
wire [3:0]          L1;
encoder_0 e(
          . I_n(S_n[9:1])   ,
   
         . Y_n(L1)   
);
reg GS1;
reg [3:0] LL;
always@(*)
begin
    if ((&S_n[9:1])&S_n[0]) GS1=0;
    else begin
        GS1=1;
       if(L1==4'b0110)  LL=4'd9;
       else if(L1==4'b0111) LL=4'd8;
       else if(L1==4'b1000) LL=4'd7;
       else if(L1==4'b1001) LL=4'd6;
       else if(L1==4'b1010) LL=4'd5;
       else if(L1==4'b1011) LL=4'd4;
       else if(L1==4'b1100) LL=4'd3;
       else if(L1==4'b1101) LL=4'd2;
       else if(L1==4'b1110) LL=4'd1;
       else if(S_n[0]==0)   LL=4'd0;
    end 
end 
assign L=LL;
assign GS=GS1;
endmodule