04-02-2013, 11:30 AM
PROGRAMS: TWO-INPUT LOGIC GATES
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THEORY:
AND: The AND gate is an electronic circuit that gives a high output (1)
only if all its inputs are high. A dot (.) is used to show the AND operation
i.e. A.B. Bear in mind that this dot is sometimes omitted i.e. AB
OR: The OR gate is an electronic circuit that gives a high output (1) if one
or more of its inputs are high. A plus (+) is used to show the OR operation.
NOT: The NOT gate is an electronic circuit that produces an inverted
version of the input at its output. It is also known as an inverter. If the input
variable is A, the inverted output is known as NOT A. This is also shown as
A', or A with a bar over the top, as shown at the outputs. The diagrams below
show two ways that the NAND logic gate can be configured to produce a
NOT gate. It can also be done using NOR logic gates in the same way.
NAND: This is a NOT-AND gate which is equal to an AND gate followed
by a NOT gate. The outputs of all NAND gates are high if any of the inputs
are low. The symbol is an AND gate with a small circle on the output. The
small circle represents inversion.
NOR: This is a NOT-OR gate which is equal to an OR gate followed by a
NOT gate. The outputs of all NOR gates are low if any of the inputs are
high.
The symbol is an OR gate with a small circle on the output. The small circle
represents inversion.
EX-OR: The 'Exclusive-OR' gate is a circuit which will give a high output
if either, but not both, of its two inputs are high. An encircled plus sign ( )
is used to show the EOR operation.
EX-NOR: The 'Exclusive-NOR' gate circuit does the opposite to the EOR
gate. It will give a low output if either, but not both, of its two inputs are
high. The symbol is an EXOR gate with a small circle on the output. The
small circle represents inversion.