My presentation about Serial Data Communication based on book, "Data Acquisition for Instrumentation and Control Systems - John Park, Steve Mackay"

1. Serial Data Communication
MADE BY:
ARNOVIA CHRISTINE SABATIANA
MARTHA MAULINA
RIZALDI SATRIA NUGRAHA
POLITEKNIK NEGERI BANDUNG
REFRIGERATION AND AIR CONDITIONING ENGINEERING

2. MIND MAP

3. DEFINITION OF SERIAL DATA COMMUNICATION
COMMUNICATION
SOURCE RECEIVER
LINK
Both the receiver and the transmitter must agree on a number of different
factors to allow successful communications between them, the most
important being:
• The type of electrical signals used to transmit the data
• The type of codes used for each symbol being transmitted
• The meaning of the characters
• How the flow of data is controlled
• How errors are detected and corrected

4. TRANSMISSION MODE

5. CODING OF MESSAGE
Encoding is the process of converting the message
data into a standard binary code for transfer over the
data communications link. The number of bits in a
code determines the total number of unique
characters that are possible.

6. ASCII (American Standard Code for Information
Interchange) is the most commonly used code for
encoding characters for data communications. It is a
7-bit code with only 2^7 = 128 possible
combinations of the seven binary digits (bits).
Each of these 128 codes is assigned to a specific
control code or character, as specified by the these
standards:
 • ANSI – X3.4
 • ISO – 646
 • CCITT alphabet #5

9. FORMAT OF DATA COMMUNICATION MESSAGE
Data is usually arranged in a particular format, with additional information
added so that the message can be effectively transmitted and understood at the
receiving end. In summary, the optional settings for asynchronous
transmission of characters are:
• Start bits 1
• Data bits 5, 6, 7, 8
• Parity bits even, odd, mark, space or none
• Stop bits 1, l½ or 2
As there cannot be half a bit, 1½-stop bits means that the mark length is 50%
longer than for one stop bit.

10. DATA TRANSMISSION SPEED
The maximum rate at which data can be transferred from
the source to the receiver on a com-munications interface
depends on a number of factors:
 • Type and complexity of the circuitry at each end
(interface)
 • Communication link (twisted-pair, coaxial cable, radio
etc)
 • Distance between the sender and receiver
 • Amount of data being transferred
 • The overhead associated with the data transfer
 • The acceptable rate of error

11. RS-232-C INTERFACE STANDARD
In telecommunications, RS-232 is the traditional name
for a series of standards for serial binary single-
ended data and control signals connecting between
a DTE (Data Terminal Equipment) and a DCE (Data
Circuit-terminating Equipment). It is commonly used
in computer serial ports.
The EIA-232 standard consists of three major
components, which define:
• Electrical signal characteristics
• Interface mechanical characteristics
• Functional description of the interchange circuits

12. ELECTRICAL
SIGNAL
CHARACTERISTIC
At the RS-232 receiver
the following signal
voltage levels are
defined:
• +3 V to +25 V for
transmission of logic 0
• –3 V to –25 V for
transmission of logic 1
In practice, many EIA-232 transmitters operate very
• +3 V to –3 V for an lose to their margin of safety, e.g. at +7 and –7 volts.
undefined logic level This can be acceptable for short cable runs, where it is
hoped that there will be no voltage problems.
Unfortunately, increased error rates can be expected at
the receiver because of induced external interference
voltages.

13. INTERFACE
MECHANICAL
CHARACTERISTIC
While this pin
configuration is likely to
be adhered to by
manufacturers at the
computers
communications
interface, it is possible
(and often likely) that
the data receive and
transmit lines on
remote stand-alone
systems are on different
pins of the DB-9
connector.

14. FUNCTIONAL DESCRIPTION OF INTERCHANGE SIRCUIT
Pin 1: Protective ground (shield)
Pin 2: Transmitted data (TXD)
Pin 3: Received data (RXD)
Pin 4: Request to send (RTS)
Pin 5: Clear to send (CTS)
Pin 6: Data set ready (DSR)
Pin 7: Signal ground (common)
Pin 8: Data carrier detect (DCD)
Pin 20: DTE ready (or data terminal ready)
Pin 22: Ring indicator
Pin 23: Data signal rate selector (DSRS)

15. MAIN FEATURE
The following are some of the main features of
equipment that use the EIA-232 interface standard:
 Communication is point-to-point
 They are suitable for serial, binary, digital, data
communication (data is sent bit by bit in sequence)
 Most EIA-232-C communications data is in the ASCII
code, although that is not part of the standard
 Communication is asynchronous (fixed timing between
data bits, but variable time between character frames)
 Communication is full-duplex (both directions
simultaneously) with a single wire for each direction and
a common wire

16. RS-485 INTERFACE STANDARD
The EIA RS-485 is the most versatile of the EIA
standards, and is an expansion of the RS-422 standard.
The RS-485 standard was designed for two-wire, half
duplex, balanced multidrop communications, and allows
up to 32 line drivers and 32 line receivers on the same
line.
RS-485 provides reliable serial communications for:
• Distances of up to 1200 m
• Data rates of up to 10 Mbps
• Up to 32 line drivers permitted on the same line
• Up to 32 line receivers permitted on the same line

17. RS-485
REPEATER
The repeater is a two-
port device that re-
transmits data received
on one side, at full
voltage levels, to the
network on the other
side.

18. COMPARISON BETWEEN TWO TYPE

19. PROTOCOL
A protocol is essential to the correct operation of the
communication system and determines a number of
important features including:
• Initialization
• Framing and frame synchronization
• Flow control
• Line control
• Error control
• Timeout control

20. FLOW CONTROL PROTOCOL
Cooperative flow control, in which the transmitter
and receiver operate under a common set of rules, is
called a flow control protocol. Below are described
the two most popular flow control protocols.
 Character flow protocols (XON/XOFF)
 Whole line protocols (ETX/ACK)

21. ASCII BASED
PROTOCOL
The ASCII protocol is
normally only used for
slow systems with one
master talking to a A simple command/response ASCII protocol, used
limited number of for communications between a personal computer
slaves. ASCII protocols and a digital transmitter is shown above.
are also popular for
stand-alone
instruments where a
serial interface has been
added, with no major
design changes, to the
existing system.

22. A variation of the short
form command and
response messages is
their long form
equivalents. To ensure
greater message
integrity, and increase
reliability, long form
messages are included
with a block checksum
at the end of the
message.

23. ERROR DETECTION
There are three popular forms of error checking used
in many protocols. These are, in order of increasing
error-detecting capability:
• Character redundancy checks
• Block redundancy checks
• Cyclic redundancy checks

24. TROUBLESHOOTING
When trouble shooting a serial data communications
interface, a logical approach needs to be followed, to
avoid wasting many frustrating hours trying to find
the problem. A procedure similar to that outlined
below is recommended:
• Check the basic parameters
• Identify which is DTE or DCE
• Clarify the needs of the hardware handshaking
• Check the actual protocol used

25. When a data communication link won’t work, the
following five very useful devices can be used to
assist in analyzing the problem:
 A Breakout Box
 Null Modem
 Loop Back Plug
 PC based protocol analyzer (including software)