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Question 31 of 40 · Digital Electronics
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NIMCET 2018

Which one of the following expressions does NOT represent the exclusive NOR of x and y?

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Answer: Option D —

Detailed Solution

1

XNOR of x and y is 1 when , i.e. , so (A) is XNOR.

2

Inverting one input of XOR inverts the output: , so (B) and (C) are XNOR.

3

Inverting both inputs changes nothing: , which is XOR, not XNOR.

✓ Check

, : XNOR is 0, but .

⚠ Common trap

(B) is the source key, but is a valid XNOR form: gives , matching XNOR.

Quick tip

Inverting one input of XOR gives XNOR; inverting both inputs cancels out and leaves XOR

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Digital Electronics — Preparation

This question tests your understanding of Digital Electronics, a key topic in the Computer Awareness section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.

Digital electronics is the study of circuits that work with binary signals, and it forms the hardware basis of every computer. This topic covers logic gates (AND, OR, NOT, NAND, NOR, XOR and XNOR) and their truth tables, Boolean algebra and its laws, De Morgan's theorems, and simplifying Boolean expressions, including with Karnaugh maps (K-maps). It also covers combinational circuits such as half adders, full adders, multiplexers, demultiplexers, encoders and decoders, and sequential circuits such as flip-flops (SR, JK, D and T), registers and counters. Exam questions test writing or reading truth tables, simplifying expressions, and identifying the output of a given circuit. Remember that NAND and NOR are universal gates, which means any other gate can be built using only NAND gates or only NOR gates. Practise the digital electronics questions below, each with a step-by-step solution.

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