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Logic Gates Extras

 

OR/NOR Gates

 

The OR and NOR gates perform opposite operations, they both can have two or more inputs but only a single output.

 

OR Gate

The function of an OR gate is to add all the values of the input and then output the sum. This means that if either input is true (1) then the output is also true; so the output is only false (0) when both inputs are false.

The Boolean equation of the logic gate is:

X = A + B

Based on this equation we can find out all possible results of different outputs. This gate can have two or more inputs. Below is the truth table that shows the outputs for all the different input combinations for a two-input OR gate.

The truth table and Venn diagram below represent the different inputs and outputs of the gate. For more information on truth tables and Venn diagrams, click here.

Truth Table: OR Gate - 2 Inputs
Input Output
0 0 0
0 1 1
1 0 1
1 1 1

Below, we have provided GIF animations to represent the function of the gate.

OR Gate: Input = 00 OR Gate: Input = 01



OR Gate: Input = 10 OR Gate: Input = 11

Application

OR gates can be used for a variety of different application. One practical use is in doorbells. A doorbell needs to sound whenever the front or the back door button is pressed. This means that if one, or both, are pressed then the output needs to be 1. This is how an OR gate works, so an OR gate would be implemented in a doorbell system with multiple buttons.





Above is the traditional symbol that represents an OR gate.


Above is the International Electrotechnical Commission (IEC) symbol for the gate.
 
 

NOR Gate

A NOR gate, also known as a Negated OR gate, does the function of the OR gate, then negates it. This means that if the result was one it would change it to zero and vice versa. A NOR gate also has two or more inputs but only a single output. This negated function is done on the OR gate by putting a small circle at the end of it. As you can see to the right, the symbol is identical to the OR gate but with a little circle.

The Boolean equation of the logic gate is:

*The line above the A+B represents a "not" or a negation

Based on this equation we can find out all possible results of different outputs. This gate can have two or more inputs. Below is the truth table that shows the outputs for all the different input combinations for a two-input NOR gate.

The truth table and Venn diagram below represent the different inputs and outputs of the gate. For more information on truth tables and Venn diagrams, click here.

Truth Table: NOR Gate - 2 Inputs
Input Output
0 0 1
0 1 0
1 0 0
1 1 0

Below, we have provided GIF animations to represent the function of the gate.

NOR Gate: Input = 00 NOR Gate: Input = 01



OR Gate: Input = 10 NOR Gate: Input = 11

Application

A NOR gate can be used in a variety of different applications. One example of a NOR gate in use is in a mixing machine. Sensors placed on the machine sense whether there is any ingredients left in the machine or not. If any of the ingredients containers are empty and the sensor is activated(1) then the output will be 0 and the mixing will stop.





Above is the traditional symbol that represents a NOR gate.


Above is the International Electrotechnical Commission (IEC) symbol for the gate.