Industrial Data

Communication

Serial Communication
 Data communication
• Data communication involves the transfer of
information from one point to another. WiFi,
LAN/WAN, fiber/copper /radio/microwave links.
• Digital data is sometimes transferred using a
system that is primarily designed for analog
communication ie A modem.
• Communication can be serial or in parallel.
 Classic Communication Vs Networking
marshalling tray
I/O dumb devices
bar capacity

PLC

Intelligent devices
COM

PLC
field bus

but: the number of end-points remains the same !

energy must be supplied to smart devices
 Marshalling

The marshaling is the

interface between the
PLC and the
instrumentation.

The field-bus replaces

the marshaling bar
Geographical extension of industrial plants
The field bus requirements follow the physical extension of the
plant:
1 km .. 1000 km Transmission & Distribution
Control and supervision of large distribution networks:
• water - gas - oil - electricity - ...
1 km .. 5 km Power Generation
Out of primary energy sources:
• waterfalls - coal - gas - oil - nuclear - solar - ...
50 m .. 3 km Industrial Plants
Manufacturing and transformation plants:
• cement works - steel works - food silos - printing - paper
pulp processing - glass plants - harbors - ...
500m .. 2 km Building Automation
• energy - air conditioning - fire - intrusion - repair - ...
1 m .. 1 km Manufacturing
flexible manufacturing cells - robots
1 m .. 800 m Vehicles
• locomotives - trains - streetcars - trolley buses - vans -
buses - cars - airplanes - spacecraft - ...
 RS-232 Communication
• Data Communication Equipment DCE transmits or
receives analogue or digital signals through a network.
• DCE works at the physical layer of the OSI model
taking data generated by Data Terminal Equipment
(DTE)
• DCE example is a modem can work as a translator of
digital and analogue signals.
 RS-232 interface standard

• The RS-232 standard consists of three

major parts, which define:
– Electrical signal characteristics
– Mechanical characteristics of the interface
– Functional description of the interchange
circuits
 So What is RS-232?
• RS-232 is a standard by which two serial
devices communicate:
– The connection must be no longer than 50
feet.
– Transmission voltages are –15V and +15V.
– It is designed around transmission of
characters (of 7 bits of length = ASCII code).
USASCII Code Chart
 RS-232 (…cont’d)
• One important aspect of RS-232 is that it is an
asynchronous form of communication.
• Asynchronous communication is important
because it is efficient;
• if no data needs to be sent, the connection is
“idle.” No additional CPU overhead is required
for an idle serial line.
 Logical Voltages
• RS-232 is a little non-intuitive at first
• Logical 1 is –15VDC
• Logical 0 is +15VDC
• When the connection is idle, the hardware ties
the connection to logical 1
• RS-232 communication is dependent on a set
timing speed at which both pieces of hardware
communicate. RS-232 also specifies the use of
“start” and “stop” bits
 RS-232 PROTOCOL
• There must be mutual agreement on how data is to be
encoded, i.e. The structure in which devices
communicate is known as a protocol.
 Sending One Character

• Every time a character is sent, the same

communication occurs:
1. Start bit sent. logical 0 ie +15VDC.
2. Seven data bits sent ( ASCII Code).
3. Stop bit sent. logical 1. –15VDC.

• This communication is dependent on the fact

that both devices are sampling the bits at the
same rate!
A Sample Transmission

7 bit ASCII code for 1011 010

 To Communicate…
• Both devices must have the same speeds to talk.
• The transmission rate of serial devices is called baud. It
is the number of bits per second.
• Most settings are read in the following form:
– Bits per second
– Number of data bits
– Parity
– Number of Stop bits
 To Communicate…
• The bandwidth is 9600 bits per second.
• Each byte has extra bits with it (start, stop, parity, etc).
• Data rate for 9600 baud would be 960 bytes per second.
 Wiring RS-232
• Common serial devices (modems for example), use a 9
pin serial connection.
 RS-232 DB9 Pin Out

Modem: DCE- Data Comm Eqpt

PC: DTE- Data Terminal Eqpt
Stop data from Modem to PC Stop data from PC to Modem
• DTR (PC) to modem • RTS (PC) to modem
• DSR (modem) to PC • CTS (modem) to PC
 What is RS-422?
• RS-422 (EIA RS-422-A Standard) is the serial connection
used on Apple Macintosh computers.
• RS-422 uses a differential electrical signal as opposed to
unbalanced signals referenced to ground with the RS-232.
• Differential transmission, which uses two lines each for
transmit and receive signals, results in greater noise
immunity and longer distances as compared to the RS-232.
• The greater noise immunity and distance are big advantages
in industrial environments.
• A maximum of ten RS422 devices can be connected in
parallel with a sender within a transmission direction
 What is RS-485?
• RS-485 (EIA-485 Standard) is an
improvement over RS-422 because it
increases the number of devices from 10
to 32.
• RS-485 defines the electrical
characteristics necessary to ensure
adequate signal voltages under
maximum load. With this enhanced multi-
drop capability, you can create networks
of devices connected to a single RS-485
serial port.
 What is RS-485? (Cont’d)
• The noise immunity and multi-drop capability
make RS-485 the serial connection of choice
in industrial applications requiring many
distributed devices networked to a PC or other
controller for data collection, HMI, or other
operations.
• RS-485 is a superset of RS-422; thus, all RS-
422 devices may be controlled by RS-485. RS-
485 hardware may be used for serial
communication for up to 4000 feet of cable.
 What is RS-485? (Cont’d)
• RS-485 was made to address the multi-
drop limitation of RS-422, allowing up to
32 devices to communicate through the
same data line.
• Any of the slave devices on an RS-485
bus can communicate with any other 32
slave devices without going through a
master device.
 Comparison of RS 232/422/485
Specifications RS-232 RS-422 RS-485
Mode of Operation Single-Ended Differential Differential
Total Number of Drivers
and Receivers on One
1 Driver 1 Driver 32 Drivers
Line.
1 Receiver 10 Receiver 32 Receivers
One driver active at a time
for RS-485 networks
Maximum Cable Length 50 ft 4000 ft 4000 ft
Maximum Data Rate (40 ft -
160 kbits/s (can
4000 ft for RS-422/
be up to 10 Mbit/s 10 Mbit/s
RS-485)
1Mbit/s)