11/18 -2

module top;

wire A, B, Cin, c1, c2, c3, sum, Cout;
system_clock #400 clock1(Cin);
system_clock #200 clock2(A);
system_clock #100 clock3(B);

xor(c1, A, B);
and(c2, A, B);
xor(sum, c1, Cin);
and(c3, c1, Cin);
xor(Cout, c3, Cin);

endmodule

module system_clock(clk);
parameter PERIOD=100;
output clk;
reg clk;

initial clk=0;

always
 begin
#(PERIOD/2) clk=~clk;
 end

always@(posedge clk)
 if($time>1000)$stop;

endmodule

11/18

module test_adder1;

 reg a,b;
 reg carry_in ;
 wire sum;
 wire carry_out;

 adder1_behavorial A1(carry_out, sum, a, b, carry_in);

 initial
  begin

    carry_in = 0; a = 0; b = 0;
    # 100 if ( carry_out != 0 | sum !== 0)
                $display(" 0+0+0=00 sum is WRONG!");
              else
                $display(" 0+0+0=00 sum is RIGHT!");
    carry_in = 0; a = 0; b = 1;
    # 100 if ( carry_out != 0 | sum !== 1)
               $display(" 0+0+1=01 sum is WRONG!");
              else
               $display(" 0+0+1=01 sum is RIGHT!");
    carry_in = 0; a = 1; b = 0;
    # 100 if ( carry_out != 0 | sum !== 1)
               $display(" 0+1+0=01 sum is WRONG!");
              else
               $display(" 0+1+0=01 sum is RIGHT!");
    carry_in = 0; a = 1; b = 1;
    # 100 if ( carry_out != 1 | sum !== 0)
                $display(" 0+1+1=10 sum is WRONG!");
              else
                $display(" 0+1+1=10 sum is RIGHT!");
    carry_in = 1; a = 0; b = 0;
    # 100 if ( carry_out != 0 | sum !== 1)
               $display(" 1+0+0=01 sum is WRONG!");
              else
               $display(" 1+0+0=01 sum is RIGHT!");
     carry_in = 1; a = 0; b = 1;
    # 100 if ( carry_out != 1 | sum !== 0)
                $display(" 1+0+1=10 sum is WRONG!");
              else
                $display(" 1+0+1=10 sum is RIGHT!");
    carry_in = 1; a = 1; b = 0;
    # 100 if ( carry_out != 1 | sum !== 0)
               $display(" 1+1+0=10 sum is WRONG!");
              else
               $display(" 1+1+0=10 sum is RIGHT!");
    carry_in = 1; a = 1; b = 1;
    # 100 if ( carry_out != 1 | sum !== 1)
               $display(" 1+1+1=11 sum is WRONG!");
              else
               $display(" 1+1+1=11 sum is RIGHT!");
    $finish;
  end
endmodule



module adder1_behavorial (carry_out, sum, a, b, carry_in);
 input a, b, carry_in;
 output carry_out, sum;


  assign sum = (~a&b&~carry_in)|(~carry_in&a&~b)|(a&b&carry_in)|(~a&~b&carry_in);
  assign carry_out = a&carry_in|a&b|b&carry_in;
endmodule

11/4 -1

module top
  integer is;
  integer ia[1:0],ib[1:0];
  reg [1:0]a,b;
  reg s
  wire [1:0]out;

  mux_behavioral mux2(out,a,b,s);

  initial
    begin
      for (is=0; is<=1; is = is + 1)
       begin
        s = is;
         for (ia[0]=0; ia[0]<=1; ia[0] = ia[0]+1)
          begin
           a[0]= ia[0];
            for (ia[1]=0; ia[1]<=1; ia[1] = ia[1]+ 1)
             begin
              a[1] = ia[1];
               for (ib[0]=0; ib[0]<=1; ib[0] = ib[0]+1)
                 begin
                   b[0] = ib[0];
                    for (ib[1]=0; ib[1]<=1; ib[1] = ib[1]+ 1)
                     begin
                      b[1] = ib[1];
                 #1 $display("a[0]=%d a[1]=%d b[0]=%d b[1]=%d s=%d out[0]%d out[1]%d",a[0],a[1],b[0],b[1],s,out[0],out[1]);
                      end
                    end
                  end
              end
         end
    end
endmodule

module mux_behavioral(OUT,A,B,SEL);
 output [1:0]OUT;
 input [1:0] A,B;
 input SEL;

mux1 X1(OUT[0],A[0],B[0],SEL);
mux1 X2(OUT[1],A[1],B[1],SEL);

endmodule

module mux1(OUT, A, B, SEL);
 output OUT;
 input A,B,SEL;

 not n1(NOT_SEL, SEL);
 and a1 (X, A, NOT_SEL);
 and a2 (Y, SEL, B);
 or  o1 (OUT, X, Y);

endmodule

11/4

module top
  integer ia,ib,is;
  reg  a,b,s;
  wire out;

  mux_structural mux1(out,a,b,s);

initial
begin
for (is=0; is<=1; is = is + 1)
begin
s = is;

for (ia=0; ia<=1; ia = ia+1)
begin
a = ia;
for (ib=0; ib<=1; ib = ib + 1)
begin
b = ib;

#1 $display("a=%d b=%d s=%d   out=%d",a,b,s,out);
end
end
end
end
endmodule

module mux_structural(OUT, A, B, SEL);
 output OUT;
 input A,B,SEL;
 not I5 (sel_n, SEL);
 and I6 (sel_a, A, SEL);
 and I7 (sel_b, sel_n, B);
 or I4 (OUT, sel_a, sel_b);
endmodule