I have a network of Modbus RTU master connected to daisy chain RTU slaves. I can't access nor modify the master controller. I need to connect a TCP controller to this network, just to read the registers of these slaves, without writing any values.
I'm currently using MGate MB3270 from MOXA; it's configured as Serial redirector. But the problem is that when I connect the TCP controller. I get unstable communication, it's drop continuously. Even when I replaced the TCP controller with Modbus poll, I receive Data error continuously.
When the TCP port is not connected, the communication is run smoothly between the master and the slaves.
You could use the ICC ETH-1000 gateway and configure its RS-485 port for Modbus RTU Sniffer and its Ethernet port for Modbus/TCP Server. This will have the least impact on your existing Modbus RTU bus.
The Modbus RTU Sniffer driver passively listens to the existing requests and responses on the Modbus RTU network and can store any register values you choose that are being read or written by the existing master.
Additional details on the ETH-1000 can be found on its product page here: