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