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Logic Gates
Logic Gates
This lesson looks at the different types of logic gates, including the action of NOT, AND, OR, NAND and NOR gates.
A digital signal operates at two levels, high or low. What else can we call them?
A logic gate is a digital electronic component that gives a particular output, depending on the input. We will look at this in more detail in this lesson.
Let's look at the output of logic gates first. What do you think 1 means?
So depending on what you put into a logic gate, you will get a different output.
If the output is that the logic gate produces a signal, it is known as a 1. If the output is that the logic gate does not produce a signal, it is known as a 0.
There are different types of logic gates: NOT, AND, OR, NAND, and NOR. Let's first have a look at what we actually mean when we say "not", "and" and "or".
Have a look at this sentence: "I have a cat AND a dog." Pick all the options that are true if this sentence is true.
You can select multiple answers
Have a look at this sentence: "It is NOT the case that I have a dog." Pick all the options that are true if this sentence is true.
You can select multiple answers
Have a look at this sentence: "My cousin has a cat OR a dog." Pick all the options that could be true.
You can select multiple answers
Look at this sentence again: "My cousin has a cat OR a dog." Is the sentence true if the cousin owns both a cat AND a dog?
So if we say NOT...
we are only talking about 1 input, for example "dog". If it's NOT a dog, then it's true. Otherwise it's false.
If we say AND...
we are talking about 2 inputs, for example "cat' and 'dog". If it's BOTH a cat and a dog, then it's true. Otherwise it's false.
If we say OR...
we are talking about 2 inputs, for example "cat" and "dog". If just one of them is a cat or a dog or if there is both a cat and a dog, then it's true. Otherwise, it's false.
Logic gates work in the same way. This logic gate only gives the output 1 if both inputs are 1. Which logic gate is that?
A) NOT gate B) AND gate C) OR gate
AND logic gates...
only give the output 1 if both input 1 AND input 2 are both 1s.
This logic gate only gives the output 1 if the input is 0. Which logic gate is that?
A) NOT gate B) AND gate C) OR gate
NOT logic gates...
only give the output 1 if the input is NOT 1 (so only if the input is 0).
This logic gate gives the output 1 as long as just one of the inputs is 1. Which logic gate is that?
A) NOT gate B) AND gate C) OR gate
OR logic gates...
give the output 1 as long as the first OR the second input is 1.
NAND is also a type of logic gate. What do you think NAND might mean?
NAND gates are the opposite of AND gates. What does that mean? Pick the most correct option.
A) NAND gates give output 1 if both inputs are 0. B) NAND gates give output 1 if 1 input is 1. C) NAND gates give output 1 if both inputs are not 1.
NOR gates mean NOT OR and they are the opposite of OR gates. What does that mean? Pick the most correct option.
A) NOR gates give output 1 if both inputs are 0. B) NOR gates give output 1 if 1 input is 0. C) NOR gates give output 1 if 1 input is 1.
To sum up!
NAND gates will give output 1 whenever an AND gate would give output 0, and NOR gates will give output 1 whenever an OR gate would give output 0.
Which logic gate has a single input and will output a signal if the input is not 1?
Which logic gate is this?
Which logic gate has two inputs and will output a signal as long as at least one input is not 1?
Which logic gate has two inputs and will output a signal as long as both inputs are 0?
Which logic gate is this?