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

Friday, October 28, 2011 , No comments

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.
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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