3.1.2. Full adder

Figure 3‑2 Full adder with truth table

A full adder can be achieved by connecting 2 half adders, according to the previous figure. It is very easy to figure out how the circuit works, from the truth table:

• SUM is 1 when the combination of inputs A, B, and Cin have an odd number of 1 values
  • it can be performed with XOR gates as follows

• CARRY (Cout) is 1
  • when inputs A and B are 1 or
  • when inputs A and B are different and the Cin value is ​​1
  • it can be performed with AND, OR, and XOR gates as follows

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