BASIC
LOGIC GATES |
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There are seven basic logic gates: AND, OR, XOR,
NOT, NAND, NOR, and XNOR. |
AND
Gate |
The AND gate is so named
because, if 0 is called "false"
and 1 is called "true," the
gate acts in the same way as the logical
"and" operator. The illustration
and table on the right side show the circuit
symbol and logic combinations for an AND
gate. (In the symbol, the input terminals
are at left and the output terminal is
at right.) The output is "true"
when both inputs are "true."
Otherwise, the output is "false."
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Input
1 |
Input
2 |
Output |
0 |
0 |
0 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
1 |
1 |
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| OR
Gate |
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Input
1 |
Input
2 |
Output |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
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The OR gate gets its
name from the fact that it behaves after
the fashion of the logical inclusive "or."
The output is "true" if either
or both of the inputs are "true."
If both inputs are "false,"
then the output is "false."
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| XOR
Gate |
The XOR (exclusive-OR)
gate acts in the same way as the logical
"either/or." The output is
"true" if either, but not
both, of the inputs are "true."
The output is "false" if both
inputs are "false" or if both
inputs are "true." Another
way of looking at this circuit is to
observe that the output is 1 if the
inputs are different, but 0 if the inputs
are the same.
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Input
1 |
Input
2 |
Output |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
0 |
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| NOT
Gate |
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A logical inverter, sometimes called
a NOT gate to differentiate it from
other types of electronic inverter devices,
has only one input. It reverses the
logic state.
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| NAND
Gate |
The NAND gate operates as an AND gate
followed by a NOT gate. It acts in the
manner of the logical operation "and"
followed by negation. The output is
"false" if both inputs are
"true." Otherwise, the output
is "true."
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Input
1 |
Input
2 |
Output |
0 |
0 |
1 |
0 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
0 |
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| NOR
Gate |
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Input
1 |
Input
2 |
Output |
0 |
0 |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
1 |
0 |
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The NOR gate is a combination OR gate
followed by an inverter. Its output
is "true" if both inputs are
"false." Otherwise, the output
is "false."
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| XNOR
Gate |
The XNOR (exclusive-NOR) gate is a combination
XOR gate followed by an inverter. Its
output is "true" if the inputs
are the same, and "false"
if the inputs are different.
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Input
1 |
Input
2 |
Output |
0 |
0 |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
1 |
1 |
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