Half-Adder
In digital electronics, a half-adder is a basic arithmetic circuit that adds two binary digits, called the input bits, and produces two output bits: the sum bit and the carry bit. A half-adder does not take into account any carry input from previous stages.

Functionality
A half-adder has two input bits, A and B. The sum bit, denoted by S, represents the addition of the two input bits without considering any carry. The carry bit, denoted by C, represents the possible carry generated by the addition of the input bits.

The truth table for a half-adder is as follows:

A B S C
0 0 0 0
0 1 1 0
1 0 1 0
1 1 0 1

In the truth table, the S column represents the sum bit and the C column represents the carry bit. From the truth table, we can see that the sum bit (S) is obtained by performing an XOR operation on the input bits (A and B). The carry bit (C) is obtained by performing an AND operation on the input bits.

Implementation
The implementation of a half-adder can be done using two logic gates: an XOR gate and an AND gate. The XOR gate takes the input bits (A and B) and produces the sum bit (S). The AND gate takes the input bits (A and B) and produces the carry bit (C).

The circuit diagram for a half-adder is as follows:

A ----\
>--- XOR ---- S
B ----/

>--- AND ---- C

The XOR gate produces the sum bit (S) and the AND gate produces the carry bit (C).

Conclusion
A half-adder is a basic arithmetic circuit that is used to add two binary digits. It produces a sum bit and a carry bit as outputs. The sum bit represents the addition of the input bits without considering any carry, while the carry bit represents the possible carry generated by the addition. The implementation of a half-adder can be done using an XOR gate and an AND gate.