Logic gates are the basic building blocks of any digital system. It is a circuit having one or more than one input and only one output. There are four main types of gate; NOT, AND, OR and XOR. There are also three gates which are the inverse of one of the main gates; NAND, NOR and XNOR. These inverse gates are the equivalent of the main gate type followed by a NOT.
== Truth Tables ==
A truth table shows all of the possible inputs and outputs for a logic circuit. The example below is for a NOT gate. It shows that if the input is a 1 then the output is a 0 and vice-versa.
== Gate Types ==
=== NOT ===
A NOT gate will invert, or flip, any input. If the input is a 1 then it will output a 0 and vice-versa.
=== AND ===
An AND gate will return a 1 if, and only if, both of the inputs were a 1. If either, or both, inputs are a 0 then the output will also be 0.
=== OR ===
An OR gate will return a 1 if either, or both, of the inputs are a 1. It will only return a 0 if both inputs were a 0.
=== XOR ===
The XOR gate will return a 1 if either, but not both, of the inputs are a 1. If both, or neither, input is a 1 then it will return 0.
=== NAND ===
The NAND gate is the same as an AND followed by a NOT, so is the inverse of an AND gate.
=== NOR ===
The NOR gate is the same as an OR followed by a NOT, so is the inverse of an OR gate.
=== XNOR ===
The XNOR gate is the same as an XOR followed by a NOT, so is the inverse of an XOR gate.
== Logic Circuits ==
A logic circuit is an electronic circuit which includes one or more logic gates. Below is an example of a logic circuit together with its logic table: