module DGate(
			// directions
			N,
			E,
			S,
			W,
			//output
			value,
			//clock status
			status //,
			// rotation
			//R
		    );

	function integer bintopol; // conversion function from binary to polarization 
	input a; //  input argument port 
case (a) 
	1'b0: bintopol = -1; 
	1'b1: bintopol = 1;
	1'bz: bintopol = 0;
	1'bx: bintopol = 0;
	endcase
	endfunction

	function Dcompute; // function definition 
	input  N, E, S, W;
	integer   polarization;
	begin
	polarization = bintopol(N) + bintopol(S) - 2*(bintopol(E) + bintopol(W));							 
if ( polarization > 1) 
	Dcompute = 1'b1;
else if  ( polarization < -1)
	Dcompute = 1'b0;
	else
	Dcompute =1'bz;
	end						  
	endfunction // Dcompute



	input N, E, S, W;
	input R;
	input [1:0] status;
	output value;
	reg value;

	parameter reset=2'b00;
	parameter switch=2'b01;
	parameter hold=2'b10;

	// //status 00=relax,01=switch, 10=hold, 11=release
	input N, E, S, W;
	input R;
	input [1:0] status;
	output value;
	reg value;

always @(status,N,E,S,W)
	begin
if (status == reset)  //reset
	value <= 1'bz;
	else if (value === 1'bz) 
	value<= #1 Dcompute(N,E,S,W);		
	end
	endmodule