Question

For a 4-bit parallel adder, if the carry-in is connected to a logical HIGH, the result is ___________

(a) The same as if the carry-in is tied LOW since the least significant carry-in is ignored

(b) That carry-out will always be HIGH

(c) A one will be added to the final result

(d) The carry-out is ignored

This question was posed to me during a job interview.

This key question is from 4-Bit Parallel Adder/Subtractor in division Arithmetic Circuits of Digital Circuits

Answer 1

Correct answer is (c) A one will be added to the final result

Explanation: For a 4-bit parallel adder, if the carry-in is connected to a logical HIGH, one will be added to the final result as a result because carry-in gives output as 1.