Hello,

I have to implement a 4-bit adder using only nmos and pmos...I am combining 3 NANDs and 3 invertors for this, but I am not allowed to put them in different modules. Here's the code I wrote:

Code:

module andmod4(in1, in2, in3, in4, out);

	input in1;
	input in2;
	input in3;
	input in4;
	output out;

	supply1 vdd;
	supply0 gnd;

	//nand(in1, in2, w1);
	pmos(w1, vdd, in1);
	pmos(w1, vdd, in2);
	nmos(w1, i1, in1);
	nmos(i1, gnd, in2);

	//inv(w1, w2);
	pmos(w2,vdd,w1);
	nmos(w2,vss,w1);

	//nand(w2, in3, w3);
	pmos(w3, vdd, w2);
	pmos(w3, vdd, in3);
	nmos(w3, i2, w2);
	nmos(i2, gnd, in3);

	//inv(w3, w4);
	pmos(w4,vdd,w3);
	nmos(w4,vss,w3);

	//nand(w4, in4, w5);
	pmos(w5, vdd, w4);
	pmos(w5, vdd, in4);
	nmos(w5, i3, w4);
	nmos(i3, gnd, in4);


	//inv(w5, out);
	pmos(out,vdd,w5);
	nmos(out,vss,w5);

endmodule
 

, but when I test it I get nothing but x and z at the output (except for the case when all inputs are 1 -> I get 1 at output).

Any ideas why this doesn't work?

Thanks,
Claudiu

Edit: the module works for only 2 bits, so I don't think NAND or the inversor is the problem, but the wiring between them (or some other aspect of Verilog that I'm not aware of)