Half-adders and full adders

• Half Adder - a circuit that performs the addition of 2 bits, taking an input of A and B and outputting the results S and the carry C

  • S column represents XOR (A XOR B)
  • C column represents AND (A AND B)
• Half Adder Cons:

  • can only take in 2 inputs so can't use the carry from a previous input.
  • can only add one-bit numbers.
• Full Adder - a circuit that joins 2 half adders with an OR gate with 3 inputs (A, B, and C-in) and 2 outputs (S and C-out).
• Full Adders are used to calculate the sum of two binary digits when there is already a carry bit present.
• Inside the Full Adder, we have two Half Adders joined by an OR Gate. This allows us to combine the carry bit from the second Half Adder with the carry bit from the first Half Adder using the OR Gate.