"Iron" ... logic!
VTS'99
I decided to "novice" does not
will contain descriptions of how to learn to solder, or the
grass circuit boards, or What is a resistor or chip. Such
information, there is plenty of form of printing books, and
once you decided to become zhelezyachnikom, will have to delve
into this literature.
(C) KLIM (MSK)
(R) VTS'99
An important feature of digital technology
is the similarity of elements and nodes,
of which are going to a variety of
devices of modern electronics,
Automation and Computer Engineering. The same principle of
building complex devices from a limited number of simple
elements are widely used in engineering.
In the digital technique any complex scheme
information processing, designed,
For example, to calculate or automatic control, can make all of
the three basic logic gates AND, OR
and NOT, and triggers. Moreover, the trigger
consists of logic elements. Consider the appointment and work.
Logic circuits.
Logical OR element simulates the operation of logical
addition, or as it also called disjunction. Algebraically, this
operation is written as follows:
C = A + B.
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 of variables A and B. Variable C must equal to 1 if A
and B are equal to 1, either individually or simultaneously.
Dependence between the binary variables A and B and C switching
functions can be defined in a truth table, in her written
truth conditions of complex statements in the
Depending on the truth of simple sentences.
A B C
----- C = 1 if
0 0 0
0 1 1 A or B = 1
1 0 1
1 1 1
Electrical circuit that implements this
function must have the output signal,
if there is a signal on at least one of the
inputs.
A
. .. A>> C
B C
U. /. @ B>
R
.
Fig.1 Fig.2
A 1> C
Fig.3 B
Figures 1 and 2 reading circuit gate or by using buttons
(1) and a diode OR gate (2). Figure 3 shows the symbol of the
element OR.
Logic element performs logical multiplication or
conjunction. Algebraically, this operation is written
as follows:
C = A * B,
while C = 1 only if
A and B are both equal to 1. These rules
can be written in the following table:
A B C
----- C = 1 if
0 0 0
0 1 0 A and B = 1
1 0 0
1 1 1
Electrical circuit corresponding
logic operations and should have a signal
output only if there are signals at the same time on all inputs.
The easiest way to this logic operation is modeled by a series
connection buttons shown in Figure 4. Obviously, the bulb C
lights up only if both are pressed knpki A and B. In Figure 5
shows the diode gate I. On
Figure 6 shows the symbol
gate I.
A B +5 v
. .. .. R
U C A <> C
. @
Figure 4 B <Fig.5
A '> C
Fig.6 B
Characteristics of the AND and OR is that for the inverse
level they perform the opposite operation. Ie OR element will
output C = 0 only if both inputs A _and_ B = 0. A element, and
shall Output C = 0 if A _ili_ B = 0. This feature is often used
in circuits with active low, for example,
Speccy and other devices on the Z80.
NOT logic element performs an operation of negation or
inversion of algebraically it can be written as follows:
_
C = A,
while output will be 1 if the input signal is 0, and vice
versa, output is equal to 0 for input 1. Work element is not
written in the following table:
A C
--- C - not A
0 1
1 0
Electrical circuit that simulates the logical NOT
operation, and the symbol this gate are shown in Figures 7 and
8. In electrical circuits, this operation is realized only
through the active elements, amplifying the signal, such as
transistors.
In addition, there is a complex logic elements AND-NOT,
NOR. In this case, their designations mark inversion (circle).
Similarly, the inversion represent and in other complex
elements.
Work of the three basic logic gates AND, OR and NOT are
best understood, Having made visual aids.
+5 V
R
Rogr 1
/> C A o> C
A>
Fig.7 Fig.8
Now we will analyze the work
Triggers.
Sometimes the trigger is the trigger circuit or flip-flop,
as he has two stable states, each
of which can be as long
while under the influence of an external signal will not be
transferred to another stable sotoyanie. Mechanical analog of
the trigger is a normal switch or toggle switch.
The simplest trigger consists of two
elements do not, inputs and outputs are connected in a ring. If
such inclusion is obtained by a scheme with two stable states.
The trigger is a unit cell memory "remembers" the flow of its
input signal of the unit. With the help of
can be modeled by one digit binary
numbers. It is obvious that to write n-bit number to n
flip-flops. For example, with using four triggers can be written
numbers from 0 to 15.
Consider the performance of two types of triggers:
RS-flip-flop and T-trigger, with wide application.
RS-flip-flop has two data
input, which receives the input signals. One input is denoted
by the letter S on the English set, meaning "plant"
while the other is the letter R from the English
reset-"dumping". Trigger denoted by the letters Q and / Q. And
the first one called the direct and the second - the inverse.
Symbol RS-flip-flop is shown
Figure 9. If the input S goes
1 signal, then the direct output appears
signal 1. This state is considered to trigger the unit.
RS-trigger T-flip-flop
S S T Q T Q
_ Clock T _
R R o Q o Q
Fig.9 Fig.10
To translate the trigger in the zero state to file a single
signal to the input R, then the direct output will be zero
signal and the output of the inversion will be a single signal.
RS-triggers are used for storing binary signals.
T-flip-flop was called by
English words tumble "oprokidovatsya"
or "flips" from the same word is the name of the "tumbler".
T-flip-flop is also called a counting trigger, as he used for
pulse counting. T-flip-flop has a count input and two inverted
and straight out. Under the action signals arriving at the
counter input, trigger changes its state from zero
on the individual and vice versa. Perebrasovany number
corresponds exactly to the number of received signals.
T-trigger is formed from RS-flip-flop with a special scheme
management. If you are connected in series
neskolko T-flip-flops, we get
electronic counter.
T-flip-flop is also a divisor
frequency by two. This is illustrated in Figure 11.
Ie first entry
Noah pulse shape clock miruet front,
and
second - you drop
Q output, and from
Fig.11 two pulses
get one.
Well, as long as enough;) The next time you will have
already shipped to me ...
isdos/03-05-99/19: 22msk
