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Logic Gates: The OR Gate

Document Reference: TN201009003 - Rev: 4.14 - Last Update: 14-11-2020 03:42 GMT - Downloaded: 26-Nov-2020 00:55 GMT

A OR gate is a logic gate with two or more inputs and one output. One or more input states must be high to produce a high output.

OR Gate Symbols

The inputs (A, B) of an OR gate are on the left, and the output (X) is on the right of the logic OR gate symbol.

Distinctive ShapeRectangular ShapeDIN Shape (Historic)
Distinctive Symbol of an OR logic-gate.Rectangle Symbol of an OR logic-gate.DIN40700 Symbol of an OR logic-gate.

OR Gate Truth Tables

Truth Table for OR Gate with 2 Inputs

ABX
000
011
101
111

Truth Table for OR Gate with 3 Inputs

ABCX
0000
0011
0101
0111
1001
1011
1101
1111

OR Gate Test-It

To test the gate, click the switch symbols in the image below.

...

OR Gate Logical Expressions

Word Equation

X = A OR B

Boolean Algebra

In boolean algebra the plus sign (+) stands for the OR operation, e.g.:

X = A + B

Alternative notation:     X = AB

ABX = A + B
00X = 0 + 0 = 0
01X = 0 + 1 = 1
10X = 1 + 0 = 1
11X = 1 + 1 = 1
ABCX = A + B + C
000X = 0 + 0 + 0 = 0
001X = 0 + 0 + 1 = 1
010X = 0 + 1 + 0 = 1
011X = 0 + 1 + 1 = 1
100X = 1 + 0 + 0 = 1
101X = 1 + 0 + 1 = 1
110X = 1 + 1 + 0 = 1
111X = 1 + 1 + 1 = 1

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