Practical Troubleshooting and Problem Solving of Modbus Protocols


The objective of this workshop is to help delegates identify, prevent and fix common industrial data communications problems focusing on the Modbus protocol. The focus is ‘outside the box’, with the emphasis on practicals that go beyond the typical communications issues and theories. The workshop’s aim is to provide delegates with the necessary toolkit of skills to solve industrial data communication problems where Modbus is used.

Modbus industrial communications systems (based on RS-232/RS-485 and Ethernet) are being installed throughout industry today, from connecting simple instruments to Programmable Logic Controllers to PCs throughout the business part of the enterprise. Communications problems range from simple wiring problems to intermittent transfer of protocol messages. Whilst the main issues with the Modbus protocol will be covered in this workshop, a clear understanding of the protocols and standards that transport Modbus protocol data units are required in order to effectively work with Modbus. This includes such standards as RS-485/RS-232 and Ethernet (preferably industrial Ethernet) and TCP/IP. Modbus, effectively one of the few (arguably, the only) industrial messaging protocols recognised by the Internet world (port 502) has one of the largest installed bases worldwide with more than 7.2 million installed nodes. The Modbus TCP/IP profile has recently been accepted by the International Electro-technical Commission (IEC) as a Publicly Available Specification (IEC PAS 62030) and is now eligible to become part of future editions of the International Standards IEC 61158 and IEC 61784-2. So it enjoys the status of a widely available open standard available to everyone. And thus the popularity. Whilst detractors will say the Modbus protocol lacks some of the refinements of the newer offerings on the market, there is no doubt that it is one of the most popular standards available in the industrial world today.

The communications system on your plant underpins your entire operation. It is critical that you have the knowledge and tools to quickly identify and fix problems as they occur, to ensure you have a secure system. No compromise is possible here. This workshop distils all the tips and tricks learnt with the benefit of many years of experience.

This workshop addresses the main issues of troubleshooting the industrial data communications network of today, enabling you to walk onto your plant or facility and troubleshoot and fix problems as quickly as possible. The focus of course being on the Modbus suite of protocols and their associated standards.


  • Receive a certificate of attendance in support of your continuing professional commitment
  • All workshops include the associated hardcopy technical manual
  • Printed workshop handouts
  • Lunch and refreshments
  • Interact and network with workshop attendees and experienced instructors
  • Practical, industry driven content to assist you in your continuing professional development (CPD)
  • Attendees automatically become IDC subscribers and receive exclusive deals and technical content every month


Anyone working with or required to troubleshoot industrial communications systems ranging from RS-232 to Fieldbus and Ethernet systems, including:


  • Consulting engineers
  • Designers
  • Design engineers
  • Electrical engineers
  • Electronic technicians
  • Instrumentation and control engineers/technicians
  • Network planners
  • Plant managers
  • Process control engineers
  • Shift electricians
  • Systems engineers
  • System integrators
  • Test engineers



  • What is Modbus?
  • Overview of the Modbus standards
  • Modbus and IDA
  • How Modbus relates to the RS-232, RS-485, Ethernet and TCP/IP standards


  • Common symptoms, problems and solutions
  • How to quickly identify likely causes
  • Basic steps
  • Communications issues
  • Grounding, shielding and noise


  • RS-232
    • Fundamentals
    • Problems: UART settings (Baud rate, parity, etc.), cabling, DTE/DCE, handshaking, voltage  levels, noise
      RS-232 practical troubleshooting session
  • RS-485
    • Fundamentals
    • Problems: cabling, common mode voltage, voltage levels, transient protection, biasing, termination, control (hardware/software), noise
      RS-485 practical troubleshooting session


  • Fundamentals: overall concept, protocol stack, client/server interaction, PDU and ADU
  • Modbus RTU vs. Modbus ASCII: frame structures and timing considerations
  • Problems: timeouts, checksums (CRC/LRC), incorrect function codes/data parameters, exception responses
    Modbus serial troubleshooting session


  • Fundamentals
  • Problems: cabling, grounding, shielding, terminators, token passing


  • Fundamentals
  • Protocol analysis
  • Problems: noise, connectors, cabling, wire types, jabber, excessive broadcasting, bad frames, faulty auto-negotiation, network loading, component failure
    Ethernet practical troubleshooting session


  • Fundamentals
  • Software utilities (ipconfig, ping, arp, tracert, netstat)
  • Protocol analysis
  • Problems: IP addresses, subnet masks, default gateways, TCP connections
    TCP/IP practical troubleshooting session


  • Fundamentals: overall concept, protocol stack
  • Packet structure: PDU, ADU, MBAP header
  • TCP connectivity issues
  • Protocol analysis
  • Modbus/TCP to Modbus serial gateways
  • Problems: TCP connection problems, timing issues
    Practical session with Modbus over TCP/IP


  • Fundamentals
  • Problems: noise, interference, power, distance, channel separation, encryption
    Practical session with Modbus/TCP over IEEE802.11


  • Summary of all the problems faced
  • Further troubleshooting tips

During this workshop there are numerous PRACTICAL SESSIONS, including:

  • RS-232 (COM port) basics
  • RS-232 point to point communications
  • RS-485 basics
  • Logging and protocol analysis on serial (RS-232/RS-485) communications system
  • Modbus Serial operation: RTU mode
  • Modbus Serial operation: ASCII mode
  • Setting up a basic Ethernet network
  • IP configuration
  • Protocol analysis on Ethernet network
  • Modbus/TCP
  • Modbus (Serial) over IEEE802.11 wireless
  • Installation and configuration of Modbus/TCP to serial communication gateway   

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