Half Adder / Full Adder

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Half Adder

The half adder circuit will do half of a binary addition of 2 1 bit binary numbers. A & B are the 2 1 bit binary values, remember the rules of binary addition:

  • 0 1's sum is 0
  • 1 1's sum is 1
  • 2 1's sum is 0 carry is 1
  • 3 1's sum is 1 carry is 1

The most common half adder is made up of two logic gates, an AND gate and a XOR gate. It has two inputs and two outputs. The two inputs are the two bits you are adding together and the two outputs are the result and a carry-on for when the output value is not large enough to display the answer.


Full Adder

The full adder is 2 half adders connected together, this will allow you to add 2 1 bit binary numbers together.

Full Adder Blocks.png

4 Bit Adder

The 4 bit adder is 4 full adders connected together to allow you to add 2 4 bit binary numbers together. A1, A2, A3, A4 represent 1 binary number, and B1, B2, B3, B4 represent the other binary number.