OR operation

Shihab Uddin Ahmed | January 19, 2017

In AND operation section I have mentioned that there are three basic Boolean operations in digital electronics and OR operation is one of them. In OR operation, if only one input is true then the output will be true. In other words with OR operation we check whether any of the inputs are true (in high state).

Boolean expression for OR operation:

boolean-expression-for-or-operation

It is read as x equals A OR B

two-input-or-gate

OR gate symbol

Two input OR gate truth table

Truth table for two input OR operation

From the truth table above we see, output x is true (1) in every combination of inputs except when both inputs are false (0). Here the ‘+’ isn’t like the addition in ordinary algebra. But it’s similar except when more than one input is 1. In that case the output is 1, as 1 is the highest possible state in digital logic. OR operation can be performed on three, four and even more inputs.

Three input OR operation truth table

Truth table for 3 input OR operation

From the truth table above we can notice, 1+1=1, and even 1+1+1=1 in OR operation.

In digital electronics OR operation is performed using digital circuit called OR gate. I have discussed that in OR gate section.

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