using modbus (not TCP) through ethernet


Thread Starter

J-F Portala

Hi listers,
I would like to connect a very small (and cheap) PLC ( TSX NANO) to a TCP/IP network. This PLC has Modbus protocol (as slave) on board. There are cheap converters (RS485 -> ethernet) and I would like to communicate through the network to the PLC in Modbus (not in modbusTCP). What about time response? Is it working ? Perhaps is it better to work through RS232 in a special protocol where there are no response time constraints.

On the PC side, the converter is considered as a COMx.

thank you for your opinion.
SoViLor company
[email protected]
Hi Jeff,

have a look at the Schneider website they have little modbus-tcp converter for rail-mounting. (products-networking-ethernet-publications-Catalogs-transparent factory)
Device: 174 CEV 300 10
For this method I think your modbus master must also have a serial connection. For the timing I think there should be no problem if you use switched ethernet. If you have hubs and maybe even router in between you never know how long your packets will travel. The master must be very tolerant then in order not to produce error messages.
hope it helps

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Cornet Laurent

The solution of the Modbus bridge/TCPIP is good
(I mean I tested it) but you cannot use TCP/IP
to transfer your program. The 174CEV module allows only to read/write values in the PLC. A good way to do it is using the OPC server from Schneider (TLXCDOFS22M).

M. Courvelle

Lantronix makes a device that would allow you to do your modbus/ethernet configuration.
It is very easy to configure if your driver
and/or software is Windows based rather than DOS
based. It is possible to do it with a DOS app,
just not as easy.