الدّوائر المنطقيّة Logic Circuits

الدّوائر المنطقيّة
Logic Circuits

هي دوائر إلكترونية electronic circuits تقوم بمعالجة المعلومات بإجراء
عمليات منطقية عليها. وهي عبارة عن توليفة من البوابات المنطقية logic
gates والقلابات flip-flops . وتكون مخرجاتها مبنية على أحكام المنطق التي
صممت لإتباعها تبعا للإشارات الكهربائية التي تستلمها كمدخلات.

في هذه المشاركة تمهيد للدارات المنطقية الرقمية وبداية
نشأتها وفي الرابط ستجدون منهج عربي مفصّل و باللغة العربية، وعرض جميل
باللغة الإنجليزية، وكذلك ورقة عمل من web ..

Digital Logic Circuit

De******ion
Digital logic is a rational process for making simple "true" or "false"
decisions ****d on the rules of Boolean algebra.

A little history of Boolean algebra
Binary logic was first proposed by 19th-century British logician and
mathematician George Boole, who in 1847 invented a two-valued system of
algebra that represented logical relationships and operations. This
system of algebra, called Boolean Algebra, was used by German engineer
Konrad Zuse in the 1930s for his Z1 calculating machine. It was also
used in the design of the first digital computer in the late 1930s by
American physicist John Atanasoff and his graduate student Clifford
Berry. During 1944 and 1945 Hungarian-born American mathematician John
von Neumann suggested using the binary arithmetic system for storing
programs in computers. In the 1930s and 1940s British mathematician Alan
Turing and American mathematician Claude Shannon also recognized how
binary logic was well suited to the development of digital computers.

Functions performed by logic circuits
"True" can be represented by a 1 and "false" by a 0, and in logic
circuits the numerals appear as signals of two different vol***es. Logic
circuits are used to make specific true-false decisions ****d on the
presence of multiple true-false signals at the inputs. The signals may
be generated by mechanical switches or by solid-state transducers. Once
the input signal has been accepted and conditioned (to remove unwanted
electrical signals, or "noise"), it is processed by the digital logic
circuits. The various families of digital logic devices, usually
integrated circuits, perform a variety of logic functions through logic
gates, including "OR,""AND," and "NOT," and combinations of these (such
as "NOR," which includes both OR and NOT)

Types of Logic Components
One widely used logic family is the transistor-transistor logic (TTL).
Another family is the complementary metal oxide semiconductor logic
(CMOS), which performs similar functions at very low power levels but at
slightly lower operating speeds. Several other, less popular families
of logic circuits exist, including the currently obsolete
resistor-transistor logic (RTL) and the emitter coupled logic (ELC), the
latter used for very-high-speed systems.

Logical Gates
The elemental blocks in a logic device are called digital logic gates.

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]

An AND gate has two or more inputs and a
single output. The output of an AND gate is true only if all the inputs
are true.
An OR gate has two or more inputs and a
single output. The output of an OR gate is true if any one of the inputs
is true and is false if all of the inputs are false.
An INVERTER has a single input and a single
output terminal and can change a true signal to a false signal, thus
performing the NOT function.
An NAND gate has two or more inputs and a
single output. The output of an NAND gate is true if any one of the
inputs is false and is false if all the inputs are true.
An NOR gate has two or more inputs and a
single output. The output of an NOR gate is true if all the inputs are
false and is false if the inputs are different.
An EXCLUSIVE OR gate has two or more inputs
and a single output. The output of an EXCLUSIVE OR gate is true if the
inputs are different and is false if the inputs are the same.

You can easily observe how the NAND gate can be emulated by two other
gates (AND , NOT). The output of the AND gate is connected to the input
of the NOT gate.
The output of the NAND gate is true if the one of the input is false.
Now let's verify: We put true and false on the inputs of the AND gate.
This gate now returns false answer (0).This false answer is the input of
the NOT gate. This gate returns true (opposite of false). You can now
see that the answer is similar to the one witch NAND returned.

Other facts
To perform a desired overall function, large numbers of logic elements
may be connected in complex circuits. In some cases microprocessors are
utilized to perform many of the switching and timing functions of the
individual logic elements. The processors are specifically programmed
with individual instructions to perform a given task or tasks. An
advan***e of microprocessors is that they make possible the performance
of different logic functions, depending on the program instructions that
are stored. A disadvan***e of microprocessors is that normally they
operate in a sequential mode, which may be too slow for some
applications. In these cases specifically designed logic circuits are
used.

From
Programming&Electronics Network

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