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Modbus course

Learn Modbus RTU and TCP the way you meet them on site. From the data model to a bus that refuses to answer.

No account, no email address, no paywall. Start at lesson 1 or jump to the part you need.

  • 21 lessons
  • about 6 hours
  • 84 quiz questions
  • Beginner to advanced

Who this is for

For installers, service engineers, system integrators and facility technicians who connect and read Modbus devices. No programming experience required. Some background in electrical work and networking helps.

How it works

Every lesson explains the idea in plain language first, then walks through a worked example, and ends with an exercise you can do yourself. The exercises use free tooling, and each one has a variant for readers without hardware at hand.

Part 1

Fundamentals

4 lessons · about 1 hour

  1. Lesson 1Learn Modbus: why a 1979 protocol still runsBeginner · 12 minCompleted
  2. Lesson 2Modbus addressing: from 40001 to the wireBeginner · 16 minCompleted
  3. Lesson 3Reading exception codes and choosing a function codeBeginner · 15 minCompleted
  4. Lesson 4How to read a Modbus datasheet, step by stepIntermediate · 18 minCompleted

Part 2

Modbus RTU

6 lessons · about 2 hours

  1. Lesson 5RS485 explained: A, B, common and terminationBeginner · 20 minCompleted
  2. Lesson 6Baud rate and parity: why 8E1 is the defaultBeginner · 16 minCompleted
  3. Lesson 7The Modbus RTU frame byte by byte, plus CRCIntermediate · 18 minCompleted
  4. Lesson 8Multiple Modbus devices on one RS485 busIntermediate · 16 minCompleted
  5. Lesson 9Read your first Modbus device with mbpollIntermediate · 22 minCompleted
  6. Lesson 10Modbus RTU troubleshooting: symptom to causeIntermediate · 20 minCompleted

Part 3

Modbus TCP

5 lessons · about 1 hour

  1. Lesson 11Port 502, the MBAP header and the unit idIntermediate · 15 minCompleted
  2. Lesson 12Modbus TCP on your network: IP, VLAN, firewallIntermediate · 16 minCompleted
  3. Lesson 13Practise Modbus TCP with a free simulatorIntermediate · 22 minCompleted
  4. Lesson 14rtuovertcp explained: what a gateway does to your frameIntermediate · 14 minCompleted
  5. Lesson 15Modbus TCP troubleshooting with WiresharkAdvanced · 20 minCompleted

Part 4

Advanced

6 lessons · about 2 hours

  1. Lesson 16Writing to a Modbus device without breaking itAdvanced · 18 minCompleted
  2. Lesson 17Word order and floats: same bytes, other valueAdvanced · 22 minCompleted
  3. Lesson 18Calculate your poll interval and bus loadAdvanced · 18 minCompleted
  4. Lesson 19Modbus security: the protocol will not helpAdvanced · 16 minCompleted
  5. Lesson 20Modbus integration: PLC, Home Assistant, cloudAdvanced · 20 minCompleted
  6. Lesson 21Modbus commissioning checklist and cheat sheetAdvanced · 18 minCompleted

Further reading in the knowledge base

Technical guides and comparisons for Modbus monitoring

All articles