## What is OR Gate | Basic Logic gates of Digital Electronics | Wiki For U

Friday, October 28, 2011
Digital Electronics,
Tech Study
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Logic gates are decision making devices in Digital Electronics. OR gate is one of these Basic gates.

This is a logic gate that has one or more inputs and only one output. Following figure shows the sign of Or gate:

This is a logic gate having two inputs and one output.

It gives high at output, if any one of inputs are high and it gives zero or low at output , when all inputs are zero (low).

This will clear from the Truth table of OR gate, given below:

It is clear from truth table that An OR gate produces 1 (High) at output when any one of inputs are high.

It produces zero (Low) at output when all inputs are 0 or low.

The illustration of OR gate can be explained with help of following circuit diagram.

In above parallel circuit, three Switch keys A, B and C are used as three inputs, and one bulb at right bottom is shown as output. When switch key will be closed, it represents a High, ON or 1 logic and when switch key is opened, it shows that input is low or 0. When the bulb will glow, it shows a high output and when it turns off, it shows a low or zero at output.

The operation of OR gate can be expressed in boolean equation. The boolean equation of OR gate having one output and two inputs is :

+ is the symbol of OR gate. But it doesn't means addition. We can't say above equation as : X is equal to A plus B. No this is wrong.

The right way is :

X is equal to A or B. Which simply tells us that output A is high when inputs A or B is high.

You may also like to Read it: What is AND Gate | Logic gates in Digital Electronics

This is a logic gate that has one or more inputs and only one output. Following figure shows the sign of Or gate:

This is a logic gate having two inputs and one output.

It gives high at output, if any one of inputs are high and it gives zero or low at output , when all inputs are zero (low).

This will clear from the Truth table of OR gate, given below:

It is clear from truth table that An OR gate produces 1 (High) at output when any one of inputs are high.

It produces zero (Low) at output when all inputs are 0 or low.

**Operation:**The illustration of OR gate can be explained with help of following circuit diagram.

In above parallel circuit, three Switch keys A, B and C are used as three inputs, and one bulb at right bottom is shown as output. When switch key will be closed, it represents a High, ON or 1 logic and when switch key is opened, it shows that input is low or 0. When the bulb will glow, it shows a high output and when it turns off, it shows a low or zero at output.

**Boolean Representation:**The operation of OR gate can be expressed in boolean equation. The boolean equation of OR gate having one output and two inputs is :

**X = A + B**

+ is the symbol of OR gate. But it doesn't means addition. We can't say above equation as : X is equal to A plus B. No this is wrong.

The right way is :

X is equal to A or B. Which simply tells us that output A is high when inputs A or B is high.

You may also like to Read it: What is AND Gate | Logic gates in Digital Electronics

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