A logic gate is an electrical system which process signals that represent TRUE or FALSE. Usually TRUE is represented by a positive supply voltage (+V) and FALSE by 0V. At any given moment, each terminal is in one of the Binary conditions, that is, either a "1" or a "0" which are represented by different voltages, eg. "1" can be +5V and "0" 0V.
The following examples are the most commonly taught gates.
NOT GATE
The output Q is not true when the input A is true and vice versa. A NOT gate is sometimes called an inverter or a logical inverter.
| Symbol |
IEC symbol |
Input A |
Output Q |
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NAND GATE
A NAND gate is an AND gate with an inverted output. The inversion is denoted by the circle on the output.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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NOR GATE
The NOR gate is a combination of an OR gate and an inverter. If both inputs are false, the output is true. Otherwise the output is false.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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XNOR GATE
The XNOR gate is the same as the XOR gate but with an inverted output. The output is true if the inputs are the same and false if the inputs are different.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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XOR GATE
The output is true if either but not both inputs are true. The output is false if both inputs are false or if both are true.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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AND GATE
The output is true if BOTH inputs are true. An AND gate can have two or more inputs. The output is true of all inputs are true.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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OR GATE
The output is true if either inputs (or both) are true.
| Symbol |
IEC symbol |
Input A |
Input B |
Output Q |
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