The document discusses serial communication and provides details on serial vs parallel communication, asynchronous vs synchronous communication, and common serial communication standards including RS-232, RS-422, and RS-485. It describes the basic components of data communication including message, sender, receiver, transmission medium, and protocol. It also explains the electrical specifications, voltage levels, pin configurations, and comparisons of the various serial communication standards.

1. SERIAL COMMUNICATION
PRESENTED TO:
ENGINEERING DEPTT SEPL.
PRESENTED BY:
MUHAMMAD FAIZAN SALEEM
ALI RAZA
Presentation # 6
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2. CONTENTS
 Data Communication
 Components of Data Communication
 Data Flow
 Serial Communication
 Parallel Communication
 Types of Serial Communication
 Standard of serial Communication
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3. DATA COMMUNICATION
“Exchange of data between two devices via some
form of transmission medium such as a wire cable”
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4. DATA COMMUNICATION COMPONENTS
 Message
 Sender
 Receiver
 Transmission medium
 Protocol
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5. Data
Flow
Simplex
Half-
Duplex
Full-
Duplex
Simplex Communication is unidirectional. Only one of the two devices
on a link can transmit and the other can only receive (e.g.
monitor and keyboard)
Half-Duplex Each station can both transmit and receive, but not at the
same time. When one device is sending, the other can only
receive, and vice versa(Walkie-talkies)
Full Duplex Both stations can transmit and receive
simultaneously.(Telephone networks) 5
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6. DATA TRANSMISSION
The transmission of binary data across a link can be
accomplished either in parallel mode or serial mode
 In parallel mode, multiple bits are sent with each
clock pulse
 In serial mode, one bit is sent with each clock
pulse
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7. TRANSMISSION ILLUSTRATION
Serial
Receiver
Transmitter
Parallel
Receiver
Transmitter
1 bit
1 word
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8. Parallel
Serial
Cost
Speed
Transmission
Amount
Transmission
Lines
Transmission
Distance
Example
Cheap
Slow
Single bit
Single line
Long distance
Modem
Expensive
Fast
8 bits (8 data lines)
Transmitter & Receiver
8 lines for simultaneous
transmission
Short distance
(synchronization)
Printer Connection
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SERIAL AND PARALLEL COMMUNICATION
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9. SERIAL COMMUNICATION
 Serial communication is the process of sending
data one bit at a time, sequentially, over a
communication channel.
Serial
Communication
Asynchronous Synchronous
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10. ASYNCHRONOUS COMMUNICATION
“Asynchronous” means the sender transmits data
using its own timing source, rather than sharing a
timer or clock with the receiver.
 Asynchronous here means "asynchronous at the
byte level but the bits are still synchronized; their
durations are the same.
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11. ASYNCHRONOUS COMMUNICATION
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The Transmitter
o Also adds the start,
stop and parity check
bits
The Receiver
o Extracts the data using
its own clock
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 Start bit—indicates the beginning of the data word
 Stop bit—indicates the end of the data word
 Parity bit—added for error detection (optional)

12. ASYNCHRONOUS COMMUNICATION
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 It is Cheap and
Effective.
 Used for long
transmission.
 Asynchronous
transmission is easy to
implement but less
efficient as it requires
an extra 2-3 control bits
for every 8 data bits
 This method is usually
used for low volume
transmission
Advantages Disadvantages
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13. SYNCHRONOUS COMMUNICATION
 In synchronous transmission, the bit stream is
combined into longer frames which may contains
multiple bytes
 It is the responsibility of the receiver to reconstruct
the information
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14. SYNCHRONOUS COMMUNICATION
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 Without start/stop bits, timing becomes very
important
 Accuracy of the received information is completely
dependent on the ability of the receiver to keep an
accurate count of the bits.
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15. SYNCHRONOUS COMMUNICATION
 Advantage of synchronous transmission is speed.
 No extra bits to introduce at the sending end and
remove at the receiving end, and, by extension,
with
 Fewer bits to move across the link,
 For this reason, it is more useful for high-speed
applications (transmission of data from one
computer to another)
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16. 16
DTE-DCE INTERFACE
 The DTE generates the data and pass them to a DCE. The DCE
converts the signal to a format appropriate to the transmission
medium
 When the signal arrives at the receiving end, this process is reversed
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17. 17
DATA TERMINAL EQUIPMENT (DTE)
 DTE includes any unit that functions either as a
source of or as a destination for binary digital
data
 It can be a computer or PLC.
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18. 18
DATA CIRCUIT-TERMINATING EQUIPMENT
(DCE)
 DCE includes any functional unit that transmits
or receives data through a network
 Commonly used DCEs include modems
Modem
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19. SERIAL COMMUNICATION PROTOCOLS
There are the following serial communication
protocols:
 EIA-232(RS-232)
 RS-422
 RS-485
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20. RS-232
Originally issued in 1962 as the RS-232 standard
(recommended standard)
Used for many purposes, such as connecting a
mouse, printer, or modem, as well as industrial
instrumentation
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21. ELECTRICAL SPECIFICATIONS
 EIA(Electronic Industries Association)-232 states
that all data must be transmitted as logical 1s and
0s
 0 defined as a positive voltage and 1 defined as a
negative voltage
 To be recognized as data, the amplitude of a signal
must fall between 3 and 25 volts or between -3 and
-25 volts
 EIA-232 allows for a maximum bit rate of 20 kbps
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22. VOLTAGE LEVEL OF RS-232
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23. RS-232
 Communication is completed using 3 transmission
lines:
 Ground
 Transmit
 Receive
 The port is able to transmit data on one line while
receiving data on another.
 Use unbalanced differential signals.
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24. EIA-232 MECHANICAL SPECIFICATION
 The EIA-232 defines the interfaces as a 25-wire
cable with a male and a female DB-25 pin
connection attached to either end. The length of the
cable may not exceed 15 meters
 A DB-25 connector is a plug with 25 pins, each of
which is attached to a single wire with a specific
function
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DB-25 Implementation
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25. EIA-232 MECHANICAL SPECIFICATION
 Another implementation of EIA-232 uses a 9-wire
cable with a mail and a female DB-9 pin connector
attached to either end
 Male connector is used on DTE and female
connector is used on DCE
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DB-9 Implementation
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26. RS-422 & RS-485
 RS-422 and RS-485 are the common names for
two serial communications standards.
 The standards, defined by the Electronics Industry
Association, are more correctly named EIA/TIA-422
and EIA/TIA-485.
 RS-422 and RS-485 communicate digital
information over twisted pair wire from transmitters
to receivers.
 Devices can be up to 4000 feet (1220 meters) apart
before repeaters are required.
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27. RS-422 & RS-485
 RS-422 drivers can transmit to up to 10 receivers.
Up to 32 RS-485 transceivers can occupy a bus.
 RS-422/485 systems can communicate at rates up
to 10 Mbps (though most systems operate at lower
bit rates).
 Both systems utilize balanced outputs and
differential inputs, which provide better noise
immunity than single-ended systems such as RS-
232.
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28. RS-422 & RS-485
 RS-422 also makes it possible to create point-to-
multipoint connections.
 In a point-to-multipoint arrangement the node
originating the data (master) can broadcast data to
several (slave) nodes at once.
 For the master to receive data back from each
slave, RS-485 devices are required.
 RS-422 and RS-485 contain balanced differential
signals.
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29. BALANCED DIFFERENTIAL SIGNALS
 Voltage produced by the driver appears across a
pair of signal lines.
 These lines produce complementary (opposite)
output signals.
 RS-422/RS-485 balanced data transmission also
requires a GND connection, even though the GND
connection is not used by the receiver to determine
the logic state of the data.
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30. VA - VB < -0.2V = "1"
VA - VB > 0.2V = "0"
Where VA and VB are the voltages on the "A" and "B"
lines respectively.
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31. 2 & 4 WIRE CONNECTIONS
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32. PIN CONFIGURATION OF RS-422/485
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33. COMPARISON OF RS-232,422 & 485
RS-232 RS-422 RS-485
Line Configuration Single Ended Multi-drop Multi-drop
Maximum Cable
Length
50 ft 4000ft 4000ft
Maximum data
Rate
20kbites/s 10Mbites/s 10Mbites/s
Typical logic
levels
+/- 5 to +/-15 V +/-2 to +/-5 +/- 1.5 to
+/-6 V
Receiver
Sensitivity
+/-3 V +/-200mV +/- 200 mV
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