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Introduction to Fundamental Logic Circuits
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-= Introduction to Fundamental Logic Circuits =-
-= By Serial =-
-= serial@digitalgenocide.net =-
-= http://www.2600slc.org =-
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In this talk I will answer the following question. What is a logic circuit? I will also give a
brief introduction into how a logic circuit functions.
Well, computer logic is defined as "The science of reasoning. In other words, it is the
development of a reasonable or logical conclusion based on known information." (www.tpub.com)
Computers operate on a True/False logic. Eg. If it is true that all computers are fast, and
the 286 is a computer, then we can form a logical conclusion that the 286 is fast.
To reach a logical conclusion you must assume a qualifying statement. You must also assume that
this statement is true.
"Lewis is heterosexual" is a true statement, therefore "Lewis likes little boys" is false. There
are no "in-the-middle" statements. The conclusion drawn is either true or false.
Variables can represent statements. Eg. "Grifter works too much." can be represented by G. If
Grifter indeed works too much, then G is TRUE. If Grifter does NOT work too much, then G is FALSE.
The complement is shown by placing a bar over the variable, and is spoken as "NOT G."
Example:
Statement Variable Conclusion Logic State
Grifter works too much G TRUE 1
Grifter does NOT work too much G FALSE 0
Example 2: Assume the inverse.
Grifter works too much G FALSE 0
Grifter does NOT work too much. G TRUE 1
Side Note ---- Logical Conditions/Logic circuits have two states 1, which represents "True,"
and 0, which represents "False."
Sometimes more than one variable will be used in an expression, such as F-U-C-K. This is spoken
as "F AND U AND NOT C AND K."
Logic circuits are typically divided into two categories based on their LOGIC POLARITY: Positive
and Negative logic.
Positive logic is when "the signal that activates the circuit (the 1 state) has a voltage level
that is more POSITIVE than the 0 state, then the logic polarity is considered to be POSITIVE.
Table 2-2 shows the manner in which positive logic may be used." (www.tpub.com)
Negative Logic is defined as follows: "If the signal that activates the circuit (the 1 state) has
a voltage level that is more NEGATIVE than the 0 state, then the logic polarity is considered to
be NEGATIVE." (www.tpub.com) "As you study logic circuits, you will see a variety of symbols
(variables) used to represent the inputs and outputs. The purpose of these symbols is to let
you know what inputs are required for the desired output. If the symbol A is shown as an input to
a logic device, then the logic level that represents A must be HIGH to activate the logic device.
That is, it must satisfy the input requirements of the logic device before the logic device will
issue the TRUE output." (www.tpub.com)
"If you consider the lamp as the output of a logic device, then the same conditions exist. The TRUE
(1 state) output of the logic device is to have the lamp lit. If the lamp is not lit, then the output
of the logic device is FALSE (0 state)." (www.tpub.com)
Thanks to www.tpub.com for format/example inspiration and definitions.
To read more on Logic Circuits, and to learn about gates and their functions -
visit www.howstuffworks.com or http://math.hws.edu/TMCM/java/labs/xLogicCircuitsLab1.html
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