Half Adder & Full Adder

Half Adder:

The half adder is an example of a simple, functional digital circuit built from two logic gates.  The half adder adds to one-bit binary numbers (AB).  The output is the sum of the two bits (S) and the carry (C). Note how the same two inputs are directed to two different gates.  The inputs to the XOR gate are also the inputs to the AND gate.  The input "wires" to the XOR gate are tied to the input wires of the AND gate; thus, when voltage is applied to the A input of the XOR gate, the A input to the AND gate receives the same voltage.



Half Adder Truth table Animation:

half adder.gif


Full Adder:

The full-adder circuit adds three one-bit binary numbers (C A B) and outputs two one-bit binary numbers, a sum (S) and a carry (C1).   The full-adder is usually a component in a cascade of adders, which add 8, 16, 32, etc. binary numbers.  The carry input for the full-adder circuit is from the carry output from the circuit "above" itself in the cascade.  The carry output from the full adder is fed to another full adder "below" itself in the cascade. If you look closely, you'll see the full adder is simply two half adders joined by an OR.

Click the picture to see a Animation

Adder - Video:

Adder - Presentation:

Arithmetic Circuits - Presentation:

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