OR Gate Truth Table

By Priyanshu Vaish|Updated : May 2nd, 2022

OR Gate Truth Table: A logic gate is a physical device that performs a logical operation in one or more logical inputs and produces a single logical output. In this article, we learn about the logical OR gate. The output of a "Logic OR Gate" only returns "LOW" again when all the inputs are "LOW". In other words, for the logic OR gate, any "HIGH" input will give a "HIGH" as output.

Thus the logic OR gate can be correctly described as an "Inclusive OR gate" because the output is true when both gate inputs are true (HIGH). Therefore, we can define the operation of a 2-input logic OR gate as:

"If either A or B is true, then Q is true."

Table of Content

What is an OR Gate?

The OR gate will have two or more inputs but only one output. The function of a logical OR gate effectively finds the maximum between two binary digits, such as the complementary AND function finds the minimum.

An OR gate can have two or more inputs, with at least one of them being true. The bits are set to one using the OR operator. The logical symbol for the OR gate is shown below:

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Thus, the logical boolean expression of the OR gate is Y = A+B.

What is the Truth Table of an OR Gate?

The truth table is a table that displays the output state based on the various combinations of input states. It demonstrates how a logic gate works. The truth table lists the output of a particular digital logic circuit for all the possible combinations of its inputs. For example, the truth table of a 2 input OR gate can be represented as:

It is clear from the truth table that if all the inputs or any of the inputs are high, the output Y is HIGH, whereas if all the inputs are LOW, then the output Y is low.

Properties of OR Gate

OR gate follows both commutative and associative laws as:
Commutative law: A + B = B+ A
Associative law: (A + B + C) = A + (B + C) = (A + B) +C

 

Enable and Disable Inputs for OR Gate

The representation of an OR gate is given below.


For control = 0;

A

Control

Y

0

0

0

1

0

1

The change in the input causes the change in the output; hence, for OR gate logic, '0' is an enable input.
For control = 1;

A

Control

Y

0

1

1

1

1

1

Due to change in the input, output remains the same; therefore for OR gate logic, '1' is a disabled input.
The switching circuit diagram for the OR gate is shown:


Here, the bulb will glow when any of the switches (either A or B) or both the switches are closed.
In a multi-input OR gate, an unused input can be connected to

  1. Logic '0' (Enable) or pull-down.
  2. Any of the user input.
  3. Left open or floating in case of ECL logic.

Out of these procedures, the best way is to connect to the logic '0' or pull down.

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FAQs

  • An OR gate is the digital logic gate with two or more inputs and one output that performs logical disjunction. The output of an OR gate is '1' when one or more of its inputs is '1'. If all of the OR gate's inputs are '0', then the output of the OR gate is '0'.

  • An OR gate is the digital logic gate that gives an output of 1 when any of its inputs are 1. otherwise 0. An OR gate performs like two switches in parallel, supplying a light so that the light is on when either of the switches is closed.

  • The logic or Boolean expression is given for a digital logic OR gate is that for Logical Addition, denoted by a plus sign, ( + ), giving us the Boolean expression of A+B = Q.

  • The logic OR gate can be correctly described as an "Inclusive OR gate" because the output is true when both gate inputs are true (HIGH). Therefore, we can define the operation of a 2-input logic OR gate as:

    "If either A or B is true, then Q is true."

  • The truth table for an OR gate is as follows:

     byjusexamprep

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