Digital Logic
Digital or binary logic has fascinated many people over the years. The very idea that a
twovalued number system can possibly be the basis for the most powerful and
sophisticated computers seems astounding, to say the least. Nevertheless, it is so, and
the how and the why of this requires some explanation.
Everything in the digital world is based on the binary number system. Numerically,
this involves only two symbols: 0 and 1. Logically, we can use these symbols or we
can equate them with others according to the needs of the moment. Thus, when
dealing with digital logic, we can specify that:
0 = false = no
1 = true
= yes
Using this twovalued logic system, every statement or condition must be either "true"
or "false;" it cannot be partly true and partly false. While this approach may seem
limited, it actually works quite nicely, and can be expanded to express very complex
relationships and interactions among any number of individual conditions.
One essential reason for basing logical operations on the binary number system is that
it is easy to design simple, stable electronic circuits that can switch back and forth
between two clearlydefined states, with no ambiguity attached. It is also readily
possible to design and build circuits that will remain indefinitely in one state unless
and until they are deliberately switched to the other state. This makes it possible to
construct a machine (the computer) which can remember sequences of events and
adjust its behavior accordingly.
Digital logic may be divided into two classes: combinational logic, in which the
logical outputs are determined by the logical function being performed and the logical
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 Winter '09
 Logic, Logic gate, logical input states, Basic Logical Functions, logical input signals

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