Question

Half-adders have a major limitation in that they cannot __________

(a) Accept a carry bit from a present stage

(b) Accept a carry bit from a next stage

(c) Accept a carry bit from a previous stage

(d) Accept a carry bit from the following stages

The question was asked in an internship interview.

This is a very interesting question from Half Adder & Full Adder topic in portion Arithmetic Circuits of Digital Circuits

Answer 1

Right choice is (c) Accept a carry bit from a previous stage

To elaborate: Half-adders have a major limitation in that they cannot accept a carry bit from a previous stage, meaning that they cannot be chained together to add multi-bit numbers. However, the two output bits of a half-adder can also represent the result A+B=3 as sum and carry both being high.