4 位元加法器

# 有號數的加法

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

adder4 DUT (a, b, 1'b0, sum, c_out);

initial
begin
a = 4'b0101;
b = 4'b0000;
end

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

initial #2000 \$finish;

endmodule```
```

## Icarus 編譯執行

``````D:\ccc101\icarus\ccc>iverilog -o sadd4 sadd4.v

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

# 無號數的加法

``````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 [3:0] a, input [3:0] b, input c_in, output [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 main;
reg [3:0] a;
reg [3:0] b;
wire [3:0] sum;
wire c_out;

adder4 DUT (a, b, 1'b0, sum, c_out);

initial
begin
a = 4'b0101;
b = 4'b0000;
end

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

initial #2000 \$finish;

endmodule```
```

## Icarus 編譯執行

``````D:\ccc101\icarus\ccc>iverilog -o adder4 adder4.v

50ns monitor: a= 5 b= 1 sum= 6
100ns monitor: a= 5 b= 2 sum= 7
150ns monitor: a= 5 b= 3 sum= 8
200ns monitor: a= 5 b= 4 sum= 9
250ns monitor: a= 5 b= 5 sum=10
300ns monitor: a= 5 b= 6 sum=11
350ns monitor: a= 5 b= 7 sum=12
400ns monitor: a= 5 b= 8 sum=13
450ns monitor: a= 5 b= 9 sum=14
500ns monitor: a= 5 b=10 sum=15
550ns monitor: a= 5 b=11 sum= 0
600ns monitor: a= 5 b=12 sum= 1
650ns monitor: a= 5 b=13 sum= 2
700ns monitor: a= 5 b=14 sum= 3
750ns monitor: a= 5 b=15 sum= 4
800ns monitor: a= 5 b= 0 sum= 5
850ns monitor: a= 5 b= 1 sum= 6
900ns monitor: a= 5 b= 2 sum= 7
950ns monitor: a= 5 b= 3 sum= 8
1000ns monitor: a= 5 b= 4 sum= 9
1050ns monitor: a= 5 b= 5 sum=10
1100ns monitor: a= 5 b= 6 sum=11
1150ns monitor: a= 5 b= 7 sum=12
1200ns monitor: a= 5 b= 8 sum=13
1250ns monitor: a= 5 b= 9 sum=14
1300ns monitor: a= 5 b=10 sum=15
1350ns monitor: a= 5 b=11 sum= 0
1400ns monitor: a= 5 b=12 sum= 1
1450ns monitor: a= 5 b=13 sum= 2
1500ns monitor: a= 5 b=14 sum= 3
1550ns monitor: a= 5 b=15 sum= 4
1600ns monitor: a= 5 b= 0 sum= 5
1650ns monitor: a= 5 b= 1 sum= 6
1700ns monitor: a= 5 b= 2 sum= 7
1750ns monitor: a= 5 b= 3 sum= 8
1800ns monitor: a= 5 b= 4 sum= 9
1850ns monitor: a= 5 b= 5 sum=10
1900ns monitor: a= 5 b= 6 sum=11
1950ns monitor: a= 5 b= 7 sum=12
2000ns monitor: a= 5 b= 8 sum=13```
```