DATA TRANSFER
ON A COMPUTER
(C) Mg.Beeper/Last Masters
-------------------------------------------------------
Data transmission is a very broad concept.
tie covering the entire transport process
calculating information (using a computer
technology) from one point to another. For
so that two or more computers
could exchange data with each other,
it is necessary to establish a number of rules that
they must follow. These rules, or
as they are also called, interfaces and protocols
cola, determine electrical, physical
Kie and functional characteristics of the lines
communications.
There are two most important
class of interfaces: parallel and serial
positive. Parallel are characterized
simultaneous transmission of several bits over
separate communication lines. Their advantage
lies in high transmission speed
information. They are used as usual
lo, for domestic or local transmission
data. Parallel communication is used
to transmit informationinside the computer
ra. Typical parallel interfaces
are the internal buses of the computer, used
used to transmit addresses and data.
Parallel interfaces are often used -
for communication with high-speed printing
melting devices, usually on non-
long distances (2-3m).
Many devices transmit information
sequentially, i.e. one bit at a time. For
transmission uses a communication line that
paradise may be in one of two possibilities.
possible states: "parcel" state
(MARK), which determines the transmission level
no logical unit and "pause" state
(SPACE), which determines the transmission
logic zero level. So physical
the communication line can be a regular two-wire
water line, presence of potential or current
a certain value in which the corresponding
corresponds to one of the states. It may
be a telephone or radio channel, co-
the value of which corresponds to the transfer
signal of a certain frequency. For example,
"1" -1000 Hz, "0" -2000 Hz.
The most common mode of post-
investigative data transmission is
asynchronous. It is characterized by the fact that
before each word (code) having
usually length from 5 to 8 information
bits, a start bit equal to
"0" - "pause", and after the information bi-
tov - one or more stop bits,
equal to "1"- "parcels". Between words
communication lines are constantly transmitted "message"
ki" (i.e. stop bits). As a result,
It is clear that every transmitted word is limited
with start and stop bits,
receiving device, accepting the next
word, each time synchronized
in. Thanks to this, different
high spacing between words.
The data enters the communication channel, starting
starting from the least significant digit and ending
are determined by transmitting the most significant
row. After transmitting the last information
national bit can be transmitted as follows:
called parity or parity bit. Know-
parity bit value for each transmission
of the word being chosen is chosen so that it
the total number of units in a word, extended
but with this extra bit, it was even
numeric (EVEN) or odd (ODD). Use
Setting the parity bit allows you to check
every word received. If during re-
there was a failure and the bit that constituted
the word was received incorrectly, then the check
rity will indicate the presence of an error. Length
data words, parity type and minimum
number of stop bits allowed between
words (one, one and a half or two) change
from system to system over a wide range.
Baud rate is measured in baud and
bits per second. Baud is a discrete number
different line states in one second. If
at any timetime may be one of
two possible states, then both speeds
match. For the considered sequence
In practical terms, these terms are equivalent.
When organizing data transfer, it is important
choice of procedure regulating the process of communication
data exchange. The choice of procedure determines-
with the capabilities of hardware to exchange
on the data and the number of lines that
can be used to connect devices
st. The most commonly used procedures are
ry duplex and half-duplex exchange.
In duplex exchange, the receiver and transmitter
chik can be simultaneously transmitted to each other
friend data. In half-duplex mode, re-
the sensor and receiver cannot transmit
data at the same time, so they transmit it
each other in turn. In that case
the exchange procedure is regulated by special
our control lines or transmitted
on one line by special managers
"reception/transmission" codes.
It should be noted that the method is followed
transfer of information more than 150
years It was used already in 1866 on
the first intercontinental telegraph line
research on connections between Europe and America and with
from that time has reached us almost unchanged
neniya. Terms: "most significant bit", "stop bit"
bit", "baud rate" - unas-
studied from that early transmission technique
data. In the name of Emile Baudot (1845-1903),
French inventor of the first cartraf system based on sequential
nal transmission and using five-bit
code, called widespread
telegraph code and unit of transmission speed
chi information. Still everywhere
mechanical telegraphs are common
devices using the Baudot code and start-
stop exchange. And basically the amateur radio
teletypewriter (RTTY) is also based on
Tibit telegraph code and start-stop
protocol at 45.45 baud.
The development of computer technology has led
to the need to use the method
serial transmission for information exchange
formation between computer systems.
However, the simplest telegraph code and
the protocol turned out to be clearly insufficient due to
because the five-bit code does not allow
encode all the necessary characters and
signs and due to the fact that the protocol does not provide
Seals control of the communication process. By-
phenomenon of telecommunication devices
background lines - modems - required
development of interface standards
computer communications. Standard interface
V.24 adopted by the International Consultative
Committee on Telephony and Telegraphy (CCITT)
and the national
RS-232 (USA) and C2 (CIS) standards.
Most
quality of computer systems serial
data transfer. The interface providesdata transmission over unbalanced lines
communications over relatively short distances
niya (tens and hundreds of meters) with low
speeds (up to 20,000 Baud). V.24 interface
used to connect peripheral
devices: modems, printing devices
etc.
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