Programming and Development

Half Adder module half_adder ( A,B,S,C ); output S ; output C ; input A ; input B ; assign S = A ^ B; assign C = A & B; endmodule Testbench module halfadder_tb; wire t_s,t_c;   reg t_a, t_b; orgate my_gate( .a(t_a), .b(t_b), .s(t_s), .c(t_c)); i nitial begin   $monitor (t_a, t_b, t_s,t_c);   t_a = 1'b0; t_b = 1'b0; #5 t_a = 1'b0; t_b = 1'b1; #5 t_a = 1'b1; t_b = 1'b0; #5 t_a = 1'b1; t_b = 1'b1; end endmodule

VHDL code for Full adder using half adder                       half_adder.vhdl ENTITY half_adder IS --- Half Adder PORT(A,B: IN BIT ; S, Cout : OUT BIT); END full_adder; ARCHITECTURE half_adder_beh OF half_adder IS BEGIN S <= A xor B; Cout <= A and B; END full_adder_beh;   or_gate.vhdl ENTITY or_gate IS PORT(A,B: IN BIT ; C : OUT BIT); END or_gate; ARCHITECTURE or_gate_beh OF or_gate IS BEGIN C <= A or B; END or_gate_beh;     full_adder.vhdl ENTITY full_adder IS --- Full Adder PORT(A,B,Cin: IN BIT ; S, C : OUT BIT); END full_adder;  ARCHITECTURE str OF full_adder IS --component Declaration Component half_adder IS PORT(A,B: IN BIT ; S, Cout : OUT BIT); END Component; Component or_gate IS PORT(A,B: IN BIT ; C : OUT BIT); END Component; signal s1,c2,c3:std_logic;  BEGIN X1: ha...

Half Adder Half adder is a combinational  arithmetic circuit that adds two numbers and produces a sum bit (S) and carry bit (C) as the output. If  A and B are the input bits, then sum bit (S) is the X-OR of A and B  and the carry bit (C) will be the AND of A and B. From this it is clear that a half adder circuit can be easily constructed using one X-OR gate and one AND gate. Half adder is the simplest of all adder circuit, but it has a major disadvantage.  The half adder can add only two input bits (A and B) and has nothing to do with the carry if there is any in the input. So if the input to a half adder have a carry, then it will be neglected it and adds only the A and B bits. That means the binary addition process is not complete and that’s why it is called a half adder. The truth table, schematic representation and XOR//AND realization of a half adder are shown in the figure below. CODE ENTITY half_adder IS --- Half Adder PORT(a,b:in s...