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We will build a SCADA system using Modbus/TCP Protocol. SCADA Host (SCADA software) will be client and read data from PLC/RTUs, which are thought to be servers. However, RTU/PLCs need to communicate with each other also. So, for an RTU/PLC, is it possible to open double socket/channel (via ethernet port) one will treat as Client and the other will treat as Server? Or will we need 2 ethernet ports for this purpose?

Best Regards,

Okan Benli

Hello,
Sometimes nomenclature can get mixed up.

Ethernet is the media and does not care about the protocol.

I have a PC with an Ethernet port and some software that acts as a MODBUS master and connects to a device (XYZ) that acts as a MODBUS slave.

If the device (XYZ) is capable, it can act as a MODBUS master and connect to a MODBUS slave.

A device can be a master, slave or master/slave.

It would be normal for the device to allow all communications through one Ethernet connection.

The PC I am typing this on will communicate with MODBUS masters, MODBUS slaves, AB EtherNet/IP, Automation Direct, etc all at the same time.

It comes down to the software of the device. Ethernet will not be the limitation other than physical connections. (needing a hub or switch, etc)

Hope that helps.

Cheers,
Mark
www.hmisys.com