All digital systems can be constructed
by only three basic logic gates. These basic gates are called the AND gate,
the OR gate, and the NOT gate. Some textbooks also include the NAND gate,
the NOR gate and the EOR gate as the members of the family of basic logic
gates. The description of the operations of these gates are listed below
[Ref.2]:
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AND gate
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The AND gate is a circuit which gives
a high output (logic 1) if all its inputs are high. A dot ()
is used to indicate the AND operation. In practice, however, the dot is
usually omitted.
-
OR gate
-
The OR gate is a circuit which gives
a high output if one or more of its inputs are high. A plus sign (+) is
used to indicate the OR operation.
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NOT gate
-
The NOT gate is a circuit which produces
at its output the negated (inverted) version of its input logic. The circuit
is also known as an inverter. If the input variable is A, the inverted
output is written as .
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NAND gate
-
The NAND gate is a NOT-AND circuit
which is equivalent to an AND circuit followed by a NOT circuit. The output
of the NAND gate is high if any of its inputs is low.
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NOR gate
-
The NOR gate is a NOT-OR circuit which
is equivalent to an OR circuit followed by a NOT circuit. The output of
the NOR gate is low if any of its inputs is high.
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EOR gate
-
The Exclusive-OR gate is a circuit
which gives a high output if either of its two inputs is high, but not
both. A encircled plus sign () is
used to indicate the EOR operation.
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