加減器

mm117777

程式：addSub4.v
module fulladder (input a, b, c_in, output sum, c_out);
wire s1, c1, c2;

xor g1(s1, a, b);
xor g2(sum, s1, c_in);
and g3(c1, a,b);
and g4(c2, s1, c_in) ;
xor g5(c_out, c2, c1) ;

endmodule

module adder4(input signed [3:0] a, input signed [3:0] b, input c_in,
              output signed [3:0] sum, output c_out);
wire [3:0] c;

fulladder fa1(a[0],b[0], c_in, sum[0], c[1]) ;
fulladder fa2(a[1],b[1], c[1], sum[1], c[2]) ;
fulladder fa3(a[2],b[2], c[2], sum[2], c[3]) ;
fulladder fa4(a[3],b[3], c[3], sum[3], c_out) ;

endmodule

module xor4(input [3:0] a, input [3:0] b, output [3:0] y);
  assign y = a ^ b;
endmodule

module addSub4(input op, input signed [3:0] a, input signed [3:0] b,
               output signed [3:0] sum, output c_out);

wire [3:0] bop;

xor4 x1(b, {op,op,op,op}, bop);
adder4 a1(a, bop, op, sum, c_out);

endmodule

module main;
reg signed [3:0] a;
reg signed [3:0] b;
wire signed [3:0] sum;
reg op;
wire c_out;

addSub4 DUT (op, a, b, sum, c_out);

initial
begin
  a = 4'b0101;
  b = 4'b0000;
  op = 1'b0;
end

always #50 begin
  op=op+1;
  $monitor("%dns monitor: op=%d a=%d b=%d sum=%d", $stime, op, a, b, sum);
end

always #100 begin
  b=b+1;
end

initial #2000 $finish;

endmodule
Icarus 編譯執行結果
D:\ccc101\icarus\ccc>iverilog -o addSub4 addSub4.v

D:\ccc101\icarus\ccc>vvp addSub4
        50ns monitor: op=1 a= 5 b= 0 sum= 5
       100ns monitor: op=0 a= 5 b= 1 sum= 6
       150ns monitor: op=1 a= 5 b= 1 sum= 4
       200ns monitor: op=0 a= 5 b= 2 sum= 7
       250ns monitor: op=1 a= 5 b= 2 sum= 3
       300ns monitor: op=0 a= 5 b= 3 sum=-8
       350ns monitor: op=1 a= 5 b= 3 sum= 2
       400ns monitor: op=0 a= 5 b= 4 sum=-7
       450ns monitor: op=1 a= 5 b= 4 sum= 1
       500ns monitor: op=0 a= 5 b= 5 sum=-6
       550ns monitor: op=1 a= 5 b= 5 sum= 0
       600ns monitor: op=0 a= 5 b= 6 sum=-5
       650ns monitor: op=1 a= 5 b= 6 sum=-1
       700ns monitor: op=0 a= 5 b= 7 sum=-4
       750ns monitor: op=1 a= 5 b= 7 sum=-2
       800ns monitor: op=0 a= 5 b=-8 sum=-3
       850ns monitor: op=1 a= 5 b=-8 sum=-3
       900ns monitor: op=0 a= 5 b=-7 sum=-2
       950ns monitor: op=1 a= 5 b=-7 sum=-4
      1000ns monitor: op=0 a= 5 b=-6 sum=-1
      1050ns monitor: op=1 a= 5 b=-6 sum=-5
      1100ns monitor: op=0 a= 5 b=-5 sum= 0
      1150ns monitor: op=1 a= 5 b=-5 sum=-6
      1200ns monitor: op=0 a= 5 b=-4 sum= 1
      1250ns monitor: op=1 a= 5 b=-4 sum=-7
      1300ns monitor: op=0 a= 5 b=-3 sum= 2
      1350ns monitor: op=1 a= 5 b=-3 sum=-8
      1400ns monitor: op=0 a= 5 b=-2 sum= 3
      1450ns monitor: op=1 a= 5 b=-2 sum= 7
      1500ns monitor: op=0 a= 5 b=-1 sum= 4
      1550ns monitor: op=1 a= 5 b=-1 sum= 6
      1600ns monitor: op=0 a= 5 b= 0 sum= 5
      1650ns monitor: op=1 a= 5 b= 0 sum= 5
      1700ns monitor: op=0 a= 5 b= 1 sum= 6
      1750ns monitor: op=1 a= 5 b= 1 sum= 4
      1800ns monitor: op=0 a= 5 b= 2 sum= 7
      1850ns monitor: op=1 a= 5 b= 2 sum= 3
      1900ns monitor: op=0 a= 5 b= 3 sum=-8
      1950ns monitor: op=1 a= 5 b= 3 sum= 2
      2000ns monitor: op=0 a= 5 b= 4 sum=-7