Nicron #37 05 июня 1997

Железо

Iron - logic.

           "Iron" ... logic!

(C) KLIM


   An important feature of digital technology is the uniformity
elements and nodes, which are collected from a variety of
devices of modern electronics, automation and
computing. The same principle of building complex
devices from a limited number of simple elements are widely
used in engineering.

   In the digital technique any elaborate scheme of processing
information that is used, for example, to calculate or
automatic control, can make only three
basic logic gates AND, OR and NOT, and triggers. More
indeed, the very trigger consists of logic elements. Consider 
their appointment and work.


               Logic

Logical OR element simulates the operation of logical addition,
or, as it is called, the operation of disjunction. 
Algebraically this operation is written as follows: A + B = C. 
Letters A and B denote the simple utterance, or binary 
variables, and the letter C-complex sentence, or a logic 
function. Last name indicates that the function depends on the 
switching variables A and B. Variable C should be equal to 1 if 
A and B equal to 1, either individually or simultaneously. 
Relationship between binary variables A and B and C switching 
functions can be given in the form of a truth table, it says 
the conditions the truth of a complex expression depending on 
the truth simple sentences.


            A B C
            ---- 0 0 0
            0 1 1
            1 0 1
            1 1 1

Electrical circuit that implements this function should have a 
signal output, if there is a signal on at least one of the 
inputs. 



   Figures 1 and 2 reading circuit logical OR element with
application buttons (1) and a diode OR gate (2). On
Figure 3 shows the symbol of the element OR.

   Logic element performs a logical
multiplication or conjunction. Algebraically, this operation
written as follows: C = A * B, while C = 1 only
If A and B both equal 1. These rules can be
written in the following table:

            A B C
            ---- 0 0 0
            0 1 0
            1 0 0
            1 1 1

Electrical circuit corresponding to the logical AND operation,
should have a signal at the output only if there
signals simultaneously on all inputs. The easiest way to this 
logical operation is modeled by a series connection of buttons

Figure 4. Obviously, the C lamp lights only in the case
if both are pressed knpki A and B. Figure 5 shows
Diode gate I. Figure 6 shows the conditional
designation gate I.



   NOT logic element performs an operation of negation or
inversion, it can be written algebraically as follows:

  _
C = A, while output will be 1 if the input is
a 0 and vice versa, the output is equal to 0 for input
signal 1. Work element is not written in the form of the 
following table:


            A C
            - 0 1
            1 0

Electrical circuit that simulates the logical NOT operation, and
symbol of this logic element is shown in
Figures 7 and 8. In electrical circuits, this operation is 
implemented only through the active elements that enhance the 
signal such as transistors.


   Work of the three basic logic gates AND, OR and NOT better
all to understand, has made visual aids.



In the next issue we will explore with the trigger - the main
element in digital technology.

[To be continued].