Question

If minuend = 0, subtrahend = 1 and borrow input = 1 in a full subtractor then the borrow output will be __________

(a) 0

(b) 1

(c) Floating

(d) High Impedance

The question was posed to me in class test.

My question is from Fast Adder & Serial Adder topic in portion Arithmetic Circuits of Digital Circuits

Answer 1

Right option is (b) 1

Easy explanation: If minuend = 0, subtrahend = 1 and borrow input = 1 in a full subtractor then the borrow output will be 1. Because on subtracting 0 and 1, one borrow is taken and it proceeds till the next step (i.e 0 – 1 – 1 = 0, borrow = 1).