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+--- Thread: W4K as modbus RTU sniffer? (/showthread.php?tid=6244)
W4K as modbus RTU sniffer? - cgn - 09.01.2026
I've a modbus RTU setup - 4 salves + 1 master. I know all the device IDs, used registers...
I'd like to visualize some of the raw data. Unfortunately the modbus master has no API for querying raw data. Due to this, I'd like to use me W4K as modbus sniffer. Has someone done something like this already? Or any better idea?
RE: W4K as modbus RTU sniffer? - Daniel - 12.01.2026
Why would you want to do it?
You can use script like this but you can't use profile and this at the same time.
https://forum.logicmachine.net/showthread.php?tid=1979&pid=16012#pid16012
RE: W4K as modbus RTU sniffer? - cgn - 12.01.2026
The Modbus protocol only allows one master, which already exists. If I add another master to the same bus, I expect communication collisions. I want to prevent that.
Instead of a sniffer, it could be an option to add an "bus free function" to your script. For the second master(=VISU) I need a poll intervall of 60sec.
RE: W4K as modbus RTU sniffer? - Erwin van der Zwart - 12.01.2026
You can use Modbus as slave -> https://kb.logicmachine.net/integration/modbus-rtu-tcp-slave/
RE: W4K as modbus RTU sniffer? - admin - 13.01.2026
Slave mode can't catch and parse responses from other slaves, only from master. It might be possible to use raw serial communication to catch requests and responses. But it's not a trivial task.