A 4-bit binary adder compromises of four Full Adders, each one calculates for each pair of bits and gets the carry from the preceding adder. The first adder has no carry input so, it has grounded the Carry input.
The two 4-bit binary numbers(suppose A & B) to be added are given to the upper and lower sequence of input pins as shown.
The output is showin as the sequence of LEDs (ON=1 / OFF=0). The output LEDs have one extra at the last, to show the carry of the addition, which can be considered the 5th bit of the resulting binary number.
