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Using RS485 to Ethernet adapter for MODBUS via Panel Ethernet


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Hi All,

I'm trying to communicate with an RS485 MODBUS device via an RS485 to Ethernet adapter (USR-TCP232-410s Serial Device Server) from my Unistream US7-B10-TR22 panel Ethernet port.  I'm only doing this because we can't source the RS485 Com module in time and the project needs to get started. 

I've been able to communicate with the device using the adapter through a MODBUS pc program so I know it works and is set up correctly, but I can't get it to work with the Unitronics panel.  The adapter shows RS485 TX signals going to the MODBUS device from the panel, but no RX signals and the device is not working.  I have the device set up as a remote slave under MODBUS>Masters>Panel Ethernet and I believe my registers, slave ID, IP address, and port settings are all correct, but I'm not sure if I'm missing something else.  I haven't been able to find how to set baud rate or error handling so maybe that's the issue?  Any suggestions on how to proceed would be greatly appreciated!

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  • MVP 2023

Have never used that USR-TCP but for what it's worth, many things I have from USR have quirks that don't let things work the way you expect.  Their "tests" that are part of the setting up programs work fine and you go "woo-hoo", but when you translate that to your job at hand, sometimes things don't happen without further delving into deeper areas of the adapter.  Documentation is sometimes "lacking".

One thing I found that sometimes made a difference is to set the unit back to default, and then write your saved version.  Don't do the write over the top of mods already done.

cheers, Aus

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So you connect a "TPC/IP to RS485 translator" to your ethernet port to communicate with a rs485 device. So you don't need to set the baud of your ethernet connection...

I had also some troubles with modbus com.....

sometimes you ask the content of 1 register, but the slave answers with a bunch of registers.... So unilogic expects a modbus receive of 4 bytes, but the slave answers with 42 bytes...

how to test -> make a modbus master of your PLC and read 1 register into a buffer......

sometimes register 300001 is at adress 0.... or at adres 1.... 

MODBUS is always exiting to program 😂😂

I think modbus developers invented the enigma coding machine....

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Thanks for the replies.  I ended up solving the issue, it was as simple as changing the adapter parameters under "Work Mode" from "None" to "ModbusTCP".  Unfortunately using the panel ethernet for Modbus seems to interfere with connecting to the panel via ethernet and being able to network it, which is a totally different problem now... 🙁

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