Communications protocol error codes (Modbus TCP, Modbus RTU, Fiber Optic TCP etc.)

BPW363 · May 9, 2023

Hi

Safety engineer here with a mechanical background. I've been looking at error codes for Ethernet TCP and Modbus TCP communications and have been wondering whether they can be used to indicate more than just the health of the communications cable, networking, etc. For example, is it possible to infer whether say a position switch (slave) has failed based on Modbus TCP error codes? I realize there may be some ambiguity but wonder if this might be a means to improve troubleshooting and increase equipment availability.

thebard3 · May 9, 2023

Short answer-
Your modbus master should provide indications whether or not a proper response to a command is received. Also, any devices I have used do provide register locations to poll for an internal error code or status.

Brad Waybright

The more you know, the more you know you don't know.

danw2 · May 10, 2023

One vendor's clear explanation of the conditions under which a Modbus slave does not return an exception code (which can relate to hardware bus issues) and the condition under which an exception code is generated.

001_Honeywell_explanation_of_responses_for_various_conditions_including_Modbus_exception_codes_m885no.jpg

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Communications protocol error codes (Modbus TCP, Modbus RTU, Fiber Optic TCP etc.)

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