2011.11.21 二位元加法器

                                                                      二位元加法器  

module top;
reg [1:0] A, B;
reg Cin;
wire[1:0] Sum;
adder2 M2(Cout, Sum, A, B, Cin);
initial
begin
A=2'd1;
B=2'd1;
Cin=1'd1;
end
endmodule
module adder2(Cout, Sum, A, B, Cin);
output Cout;
output [1:0] Sum;
input [1:0] A, B;
input Cin;
adder1 I1 (C0, Sum[0], A[0], B[0], Cin);
adder1 I2 (Cout, Sum[1], A[1], B[1], C0);
endmodule
module adder1(Cout, Sum, A, B, Cin);
output Cout,Sum;
input A,B,Cin;
and I1 (AandB, A, B);
xor I2 (AxorB, A, B);
and I3 (And1, AxorB, Cin);
or I4 (Cout, AandB, And1);
xor I5 (Sum, AxorB, Cin);
endmodule
module system_clock(clk);
paraclk;
initial
clk=0;
always
begin
#(PERIOD/2)clk=~clk;
end
always@(posedge clk)
if($time>1000)
$stop;
meter PERIOD=100;
output clk;
reg endmodule