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A logic gate is an elementary building block of a digital circuit . every terminal is in one of the two binary conditions low (0) or high (1),
represented by different voltage levels. The logic state of a terminal can, and generally does, change
often, as the circuit processes data. In most logic gates, the low state is approximately zero volts (0 V),
while the high state is approximately five volts positive (+5 V).
There are seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.
Starting with
2-input AND Gate
For a 2-input AND gate, the output Q is true if BOTH
input A “AND ” input B are both true, giving the Boolean
Expression of: ( Q = A and B ).
2-input OR (Inclusive OR) Gate
For a 2-input OR gate, the output Q is true if EITHER
input A “OR ” input B is true, giving the Boolean
Expression of: ( Q = A or B ).
NOT Gate
For a single input NOT gate, the output Q is ONLY true
when the input is “NOT ” true, the output is the inverse
or complement of the input giving the Boolean
Expression of: ( Q = NOT A ).
The NAND and the NOR Gates are a combination of the
AND and OR Gates with that of a NOT Gate or inverter.
2-input NAND (Not AND) Gate
For a 2-input NAND gate, the output Q is true if BOTH
input A and input B are NOT true, giving the Boolean
Expression of: ( Q = not(A and B) ).
2-input NOR (Not OR) Gate
For a 2-input NOR gate, the output Q is true if BOTH
input A and input B are NOT true, giving the Boolean
Expression of: ( Q = not(A or B) ).
As well as the standard logic gates there are also two
special types of logic gate function called an Exclusive-
OR Gate and an Exclusive-NOR Gate. The actions of
both of these types of gates can be made using the
above standard gates however, as they are widely
used functions, they are now available in standard IC
form and have been included here as reference.
2-input EX-OR (Exclusive OR) Gate
For a 2-input Ex-OR gate, the output Q is true if
EITHER input A or if input B is true, but NOT both
giving the Boolean Expression of: ( Q = (A and NOT B)
or (NOT A and B) ).
2-input EX-NOR (Exclusive NOR) Gate
For a 2-input Ex-NOR gate, the output Q is true if
BOTH input A and input B are the same, either true or
false, giving the Boolean Expression of: ( Q = (A and B)
or (NOT A and NOT B) ).
i hope it will b helpful .. #h9
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