Interview questions on Modbus

21. How does the data transfer occur in TCP/IP?

The complete Modbus TCP/IP Application Data Unit that is discussed above is embedded into the data field of a standard TCP frame. This TCP frame is sent via TCP to port 502, which is specifically reserved for Modbus applications.

Modbus data transfer occur in TCP/IP

22. Through which port is the Modbus data transmitter?

Modbus TCP/IP clients and servers listen and receive Modbus data via port 502

23. What is the difference between Modbus ASCII and Modbus RTU?

  • Modbus RTU mode uses binary coding and CRC error-checking.
  • Modbus ASCII messages are less efficient and use less effective LRC error checking.
  • ASCII mode uses ASCII characters to begin and end messages whereas RTU uses time gaps (3.5 character times) of silence for framing.
  • The two modes are incompatible so a device configured for ASCII mode cannot communicate with one using RTU.
  • Modbus ASCII messages require twice as many bytes to transmit the same content as a Modbus RTU message.

24. What is the maximum Modbus RTU communication?

  • RS – 232: Maximum distance of 15 meters.
  • RS – 485 & RS – 422: Maximum distance of 1200 meters.
  • TCP/IP – Can be used at any range with proper network design.

25. RS 232 and RS 485 connections.

RS 232 Pinout
RS 232
RS 485 Pinout
RS 485

Please feel free to share the interview questions on Modbus that you encountered during interviews in the comment box below.

1 thought on “Interview questions on Modbus”

Leave a Comment