The document discusses the Modbus communication protocol. It provides an overview of Modbus, including that it was created by MODICON to connect PLCs to programming tools and is now widely used for master-slave communication between intelligent devices. Modbus can be implemented over different physical layers like RS-232, RS-422, RS-485, fiber, radio or cellular networks. It also discusses the application and network layers of Modbus, addressing models, frame structures, versions (ASCII and RTU), error checking methods, and applications in industries like healthcare, transportation, and home automation.

1. MODBUS COMMUNICATION
PROTOCOL
Presented By:
Kevin Patel(17BEE060)
Praphull Kumar(17BEE069)
Priyanshu Singh(17BEE072)
Tanish Shah(17BEE083)
Jignesh Sutariya(17BEE092)
Vishva Bhatt(17BEE100)

2. OVERVIEW
• MODBUS Protocol is a messaging structure created by MODICON company to connect PLC to
programming tools.
• It is now widely used to establish master-slave communication between intelligent devices.
• MODBUS is independent of the physical layer.
• It can be implemented using RS232, RS422, or RS485 or over a variety of media (e.g. fiber, radio, cellular,
etc...).
• MODBUS is an application layer messaging protocol for client/server communication between devices
connected on different types of buses or networks.
• So Modbus is a network for connecting field devices: sensors, actuators and field controllers such as PLCs,
regulators, driver controllers etc.
• Modbus is a kind of real-time communication systems and is based on a layered structure deduced from the
seven layers OSI model.

3. APPLICATION LAYER OF MODBUS
It is currently Implemented Using:
• TCP (Transmission Control Protocol) or IP
(Internet Protocol) Over Ethernet.
• Asynchronous serial transmission over a
variety of media (wire: EIA/TIA232-E, EIA-
422, EIA/TIA485-A; fiber, radio, etc. where
TIA is Telecommunications Industry
Association and the EIA is Electronic
Industries Association.)
• MODBUS PLUS, a high speed token passing
network.

4. NETWORK ARCHITECTURE OF MODBUS
• Every type of devices (PLC, HMI, Control
Panel, Driver, Motion control, I/O Device…)
can use MODBUS protocol to initiate a
remote operation.
• The same communication can be done as
well on serial line as on an Ethernet TCP/IP
networks. Gateways allow a communication
between several types of buses or network
using the MODBUS protocol.

5. MODBUS ADDRESSING MODEL
The MODBUS application protocol defines precisely
PDU addressing rules.
• In a MODBUS PDU each data is addressed from 0 to
65535.
• It also defines clearly a MODBUS data model
composed of 4 blocks that comprises several
elements numbered from 1 to n.
• In the MODBUS data Model each element within a
data block is numbered from 1 to n.
• Afterwards the MODBUS data model has to be
bound to the device application (IEC-61131 object,
or other application model).
• The pre-mapping between the MODBUS data model
and the device application is totally vendor device
specific.

6. 1) ASCII MODE
• ASCII stands for American Standard Code for Information Exchange. In this mode each character
byte in a message is sent as 2 ASCII characters. This mode allows time intervals of up to a second
between characters during transmission without generating errors .
• ASCII mode allows time intervals of up to 1 second to occur between characters without causing
an error.
2) RTU MODE
• RTU stands for Remote Terminal unit. In this mode each 8 bit message byte contains two 4-bit
hexadecimal characters and the message is transmitted in a continuous stream.
• The main advantage of the RTU mode is that it achieves higher throughput.
The MODBUS Protocol comes in 2 versions :
TWO VERSION OF MODBUS

7. COMPARISION OF TWO VERSION OF MODBUS
Modbus ASCII
• Characters:- ASCII 0….9 and A…F
• Error check:- Longitudinal Redundancy check(LRC)
• Frame start:- character ‘:’
• Frame end:- character CR/LF
• Gaps in message:- 1 sec
• Start bits:- 1
• Data bits:- 7
• Parity:- even/odd none
• Stop :- 1 2
Modbus RTU
• Characters:- Binary 0….255
• Error check:- Cyclic Redundancy check (CRC)
• Frame start:- 3.5 chars silence
• Frame end:- 3.5 chars silence
• Gaps in message:- 1.5 times char length
• Start bits:- 1
• Data bits:- 8
• Parity:- even/odd none
• Stop:- 1 2

8. MODBUS FRAME STRUCTURE
• The Modbus frame structure is the same for requests (master to slave messages) and responses (slave
to master messages).
Address ChecksumDataFunction
Modbus ASCII
Modbus RTU
: CR LF
Address ChecksumDataFunctionsilence silence
3A Hex 0D Hex 0A Hex
• Where CR is "carriage return" means the return of the character position cursor to the left margin & LF is
"line feed" means the moving of the cursor one line down. Both are typically used as the final characters
in a single line of ASCII text.

9. ERROR CHECKING METHOD IN MODBUS
 Parity checking
Even or odd can be optionally applied to each character.
 Frame checking
LRC or CRC is applied to the entire message.
 Continuous stream
The entire message frame must be transmitted as a continuous stream. If a silent interval (more than 1.5
character times RTU mode or 1 second ASCII mode) occurs before completion of the frame, the receiving
device flushes the incomplete message and assumes that the next byte will be the address field of a new
message.
• The master is configured by the user to wait for a predetermined timeout interval before aborting the
transaction. This interval is set to be long enough for any slave to respond normally. If the slave detects
a transmission error, the message will not be acted upon.The slave will not construct a response to the
master.
• Thus the timeout will expire and allow the master's program to handle the error.

10. APPLICATION STRUCTURE OF MODBUS
Modbus Device (Slave) Modbus Device (Slave)
InternetRS-232/485
HMISCADA The main application of Modbus is in multi master-slave
to communicate between smart devices and sensors and
instruments to monitor field devices using Desktop PCs
and Human machine interfaces. Modbus is a perfect
protocol for RTU related applications where in which
wireless communication is required. That is why it is used
in endless gas and oil substation utilities. Modbus is an
industrial protocol, moreover building, infrastructure,
transportation and energy applications can also utilize the
benefits of Modbus. The common factor is the messaging
structure that all devices support.

11. APPLICATION OF MODBUS COMMUNICATION PROTOCOL
Healthcare: For automated temperature monitoring
Modbus can be used by hospital’s IT department to monitor the temperature in single interface. Data from
different floors can be directly taken via RS485 Modbus ADC devices.
Transportation: Traffic behavior detection
The abnormal behavior of traffic can be detected by the cross referring with normal traffic patterns obtained
through the Modbus TCP transactions.
Home automation: Easy transfer of data
For transferring data from different sensors used in home automation devices can be done through Modbus
protocol. Since the data can be transferred via single layer it will be much easier when we compare other
protocols.
Other Industries
Another main application of Modbus is while connecting industrial devices that need to communicate with
other automation equipment. Other major industries include Gas and oil, Renewable energy sources like
Wind, Solar, Geothermal and Hydro etc.

12. All messages are coded in hexadecimal using 4-bit ASCII characters. Modbus ASCII marks the start of each
message with a colon character " : " (hex 3A). The end of each message is terminated with the carriage
return and line feed characters (hex 0D and 0A). This allows the space between bytes to be variable making
it suitable for transmission through some modems.
Modbus ASCII is the slowest of the three protocols, but is suitable when telephone modem or radio (RF)
links are used. This is because ASCII uses characters to delimit a message. Because of this delimiting of the
message, any delays in the transmission medium will not cause the message to be misinterpreted by the
receiving device. This can be important when dealing with slow modems, mobile phones, noisy
connections, or other difficult transmission mediums.
APPLICATION OF MODBUS COMMUNICATION PROTOCOL

13. REFERENCES
• https://camatsystem.com/wp-content/uploads/2015/12/Modbus-manual-TD80.pdf
• https://en.wikipedia.org/wiki/Modbus
• https://www.csimn.com/CSI_pages/Modbus101.html
• http://www.intea.hr/downloads/introduction_to_modbus.pdf
• https://www.youtube.com/watch?v=txi2p5_OjKU
• https://www.youtube.com/watch?v=JBGaInI-TG4
• https://camatsystem.com/wp-content/uploads/2015/12/Modbus-manual-TD80.pdf