二位比较器例程module bijiao(a1,a0,b1,b0,Y,G,R); input a1,a0,b1,b0; output Y,G,R; reg Y,G,R; always@(a1 or a0 or b1 or b0) case({a1,a0,b1,b0}) 4'b0000 : begin Y<=1; G<=0; R<=0; end 4'b0001 : begin Y<=0; G<=0; R<=1; end 4'b0010 : begin Y<=0; G<=0; R<=1; end 4'b0011 : begin Y<=0; G<=0; R<=1; end 4'b0100 : begin Y<=0; G<=1; R<=0; end 4'b0101 : begin Y<=1; G<=0; R<=0; end 4'b0110 : begin Y<=0; G<=0; R<=1; end 4'b0111 : begin Y<=0; G<=0; R<=1; end 4'b1000 : begin Y<=0; G<=1; R<=0; end 4'b1001 : begin Y<=0; G<=1; R<=0; end 4'b1010 : begin Y<=1; G<=0; R<=0; end 4'b1011 : begin Y<=0; G<=0; R<=1; end 4'b1100 : begin Y<=0; G<=1; R<=0; end 4'b1101 : begin Y<=0; G<=1; R<=0; end 4'b1110 : begin Y<=0; G<=1; R<=0; end 4'b1111 : begin Y<=1; G<=0; R<=0; end endcase endmodule