3. Half Adder Discussion

• A half adder circuit has one significant drawback:

  • since pair of bits can produce an output carry,

  • in addition to the inputs A and B, we need to account for a possible carry over from a bit of the lower order of magnitude.

  • Unfortunately, half adder has no support for such carry over input by design.

• Therefore, the combination requires not two, but three inputs to make the adder circuit more useful.

• The circuit that does the entire job is called a full adder.