Arithmetic Circuits
Half adder
原題：Half adder
重點是寫一個半加器。
Verilog
module top_module(
input a, b,
output cout, sum );
assign cout = a & b;
assign sum = a ^ b;
endmodule
Full adder
原題：Full adder
重點是寫一個全加器。
Verilog
module top_module(
input a, b, cin,
output cout, sum );
assign {cout,sum} = a + b + cin;
endmodule
3-bit binary adder
需要將3個全加器串在一起。
Verilog
module top_module(
input [2:0] a, b,
input cin,
output [2:0] cout,
output [2:0] sum );
FA FA1(.a(a[0]),.b(b[0]),.cin(cin),.cout(cout[0]),.sum(sum[0]));
FA FA2(.a(a[1]),.b(b[1]),.cin(cout[0]),.cout(cout[1]),.sum(sum[1]));
FA FA3(.a(a[2]),.b(b[2]),.cin(cout[1]),.cout(cout[2]),.sum(sum[2]));
endmodule
module FA(
input a, b, cin,
output cout, sum );
assign {cout,sum} = a + b + cin;
endmodule
Adder
原題：Adder
需要將4個全加器串在一起，順便練習用generate block寫了for loop。
Verilog
module top_module (
input [3:0] x,
input [3:0] y,
output [4:0] sum);
wire [4:1]cout;
assign sum[4] = cout[4];
FA FAA(.a(x[0]),.b(y[0]),.cin(1'b0),.cout(cout[1]),.sum(sum[0]));
genvar i;
generate
for(i=1;i<4;i++)begin:block
FA FAA(.a(x[i]),.b(y[i]),.cin(cout[i]),.cout(cout[i+1]),.sum(sum[i]));
end
endgenerate
endmodule
module FA(
input a, b, cin,
output cout, sum );
assign {cout,sum} = a + b + cin;
endmodule
Signed addition overflow
練習overflow的判別，也就是兩正數相加或兩負數相減時，分別得到負數和正數，那就是發生overflow。
Verilog
module top_module (
input [7:0] a,
input [7:0] b,
output [7:0] s,
output overflow
);
assign s = a + b;
assign overflow = (a[7]&b[7]&(~s[7])) | ((~a[7])&(~b[7])&s[7]);
endmodule
100-bit binary adder
練習如何用behavioural code描述電路。
Verilog
module top_module(
input [99:0] a, b,
input cin,
output cout,
output [99:0] sum );
assign {cout,sum} = a + b + cin;
endmodule
4-digit BCD adder
練習串接BCD adder。
Verilog
module top_module (
input [15:0] a, b,
input cin,
output cout,
output [15:0] sum );
wire [3:0] co;
bcd_fadd bf1(.a(a[3:0]),.b(b[3:0]),.cin(cin),.cout(co[0]),.sum(sum[3:0]));
bcd_fadd bf2(.a(a[7:4]),.b(b[7:4]),.cin(co[0]),.cout(co[1]),.sum(sum[7:4]));
bcd_fadd bf3(.a(a[11:8]),.b(b[11:8]),.cin(co[1]),.cout(co[2]),.sum(sum[11:8]));
bcd_fadd bf4(.a(a[15:12]),.b(b[15:12]),.cin(co[2]),.cout(co[3]),.sum(sum[15:12]));
assign cout = co[3];
endmodule