How do NAND and NOR gates relate to AND and OR gates?

A NAND gate is an AND gate followed by NOT, so it gives 0 only when all inputs are 1. A NOR gate is OR followed by NOT, giving 1 only when all inputs are 0.

What is the difference between an EOR gate and an OR gate?

An EOR gate gives 1 when its two inputs are different. Unlike OR, an EOR gate gives 0 when both inputs are 1.

When does an ENOR gate give a logic 1 output?

An ENOR gate gives 1 when its two inputs are the same, either both 0 or both 1. An ENOR gate can therefore detect whether two bits are equal.

CCEA A-Level Technology and Design 8900

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Electronic Control Systems

Logic gates, truth tables and flip-flops

3 things to know
AS 1 Paper 2

Overview

AND, OR, NOT, NAND, NOR, EOR and ENOR gates, universal gates, logic for heaters and alarms, SR flip-flops from NAND gates, and PICs against hardwired logic.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe the output of an AND gate.

Key term

Describe the output of an OR gate.

Key term

What does a NOT gate do?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe the output of an AND gate.
Model answer
An AND gate gives logic 1 only when all of its inputs are at 1. Any input at 0 gives a 0 output.
2
Describe the output of an OR gate.
Model answer
An OR gate gives logic 1 when any one or more of its inputs is at 1. The output is 0 only when every input is 0.
3
What does a NOT gate do?
Model answer
A NOT gate, or inverter, has a single input. The output is always the opposite logic state to the input.
4
How do NAND and NOR gates relate to AND and OR gates?
Model answer
A NAND gate is an AND gate followed by NOT, so it gives 0 only when all inputs are 1. A NOR gate is OR followed by NOT, giving 1 only when all inputs are 0.
5
What is the difference between an EOR gate and an OR gate?
Model answer
An EOR gate gives 1 when its two inputs are different. Unlike OR, an EOR gate gives 0 when both inputs are 1.
6
When does an ENOR gate give a logic 1 output?
Model answer
An ENOR gate gives 1 when its two inputs are the same, either both 0 or both 1. An ENOR gate can therefore detect whether two bits are equal.

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