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log e • logic probe 417
log e Abbreviation of logarithm to the base e (the
NAPIERIAN LOGARITHM). Also written ln.
logic 1. In digital circuits, the mathematics dealing
with the truth or falsity of statements (represented
by variables) and their combinations. Also
see SYMBOLIC LOGIC. Generally, “truth” is represented
by the binary digit 1, and “falsity” is represented
by the binary digit 0. 2. Collectively, the
switching circuits and associated hardware for
implementing digital functions (see 1), such as
AND, NAND, NOR, OR, etc.
logical decision During a computer program run,
a choice between alternatives based on specified
conditions. For example, one alternative path in a
routine might be selected because an intermediate
result was negative.
logical diagram A schematic diagram showing the
interconnection between gates of a logic circuit.
logical equivalence The condition in which two
logical statements have identical truth value for
all possible combinations of truth value of their
constituents.
logical file A data set composing one or several
logical records.
logical implication For logical statements x and y,
the condition that y is true whenever x is true: If
x, then y.
logical operation 1. An operation using logical operators:
AND, NOR, OR, and NAND. 2. A processing
operation in which arithmetic is not involved
(e.g., a shift).
logical operator A word or symbol representing a
logic function operating on one or more operands.
Examples: NOT, OR, AND, NOR, and NAND.
logical shift A shift operation in which digits in a
word are moved to the left or right in circular fashion;
digits displaced at one end of the word are returned
at the other. Also called CYCLIC SHIFT.
logic array In logic circuits, a redundant arrangement
of identical components in a single package.
logic circuit In digital systems, a gating or switching
circuit that performs such logical operations
as AND, NAND, NOR, OR, and XOR. It can use
diodes, transistors, charge-coupled devices, tunnel
diodes, thyristors, ferroelectric elements, magnetic-core
elements, or a combination of these. It
usually consists of diodes and transistors fabricated
onto an integrated-circuit (IC) chip.
AND NOT OR
EX-OR NAND NOR
logic circuits
(or gates)
logic comparison An operation in which two operands
are compared for equal value.
logic connectives Words connecting operands in a
logic statement; the truth or falsity of the statements
can be determined from their content and
the connectives’ meanings.
logic diagram 1. A graphic representation of a
logic function (e.g., AND, NAND, NOR, OR, and
XOR). 2. The design of a device or system represented
by graphic symbols for logic elements and
their relationships.
A
B
C
AND
NOT
OR
A B C AB + C −
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
1
logic diagram and truth table
Output
logic diode See COMPUTER DIODE.
logic flowchart The logical steps in a program or
subroutine represented by a set of symbols.
logic function An expression for an operation involving
one or a combination of logic operators.
logic gate See LOGIC CIRCUIT.
logic input current In an integrated circuit, the
input current to the logic gate at a certain voltage
value.
logic input levels The range of voltages over which
the logic trip level occurs, from low to high or high
to low. It is usually expressed in volts for the low
state and the high state; for example, low is –1 to
+2 volts, high is +4 to +6 volts.
logic instruction A command to execute a logical
function.
logic level 1. One of the two logic states 0 or 1 (on
or off, high or low). 2. Of the two logic states, that
which represents the “true” condition. 3. The voltage
amplitude of digital signals in a logic system.
logic probe A test probe with a built-in amplifier
and (usually) indicating LEDs; its tip is touched
to various test nodes in a digital logic circuit to
trace logic levels and pulses.