Modbus RTU to Modbus TCP with Digi PortServer TS1 MEI


I’m trying to create a network communication into two Schneider Automation PLC.
First one is an “April 5000” with a RS485 Modbus_RTU network card.
Second one is an " TSX57-5634" with an ethernet Modbus_TCP network card.

I have a Digi PortServer TS1 MEI for making the conversion. I have configured it with IA protocol and selected Modbus RTU with coherent communication settings. Mobus TCP is the master and Modbus RTU the slave.

I’m trying to read/write variables values from the slave but without success.

I launch a read/write request from Master PLC to the digi IP. The Network LED status is blinking but nothing else matter

Have you any idea why it’s not working ?


Sorry for language mistakes, english isn’t my mother tongue…

I have heard bad things about the April RTU - as in it’s difficult to talk to successfully. However, that might not be the problem.

First, look at this web page, which shows how to see an event trace within the TS1:

This will tell you if the TS1 is trying to poll the RTU, but no response is seen - or if the configuration causes the TS1 to ignore/discard all requests.

Second step - if the trace shows the TS1 thinks it is talking is to double check the RS-485 - as the 10-pin RJ45 connector is painful when used with RS-485. You’ll probably require the RS-485 line BIAS to be enabled on the TS1 (by enabling the termination). I’ve never worked with the RS-485 on a TS product, but I’d guess you’ll need to short the “+” and “-” together for 2-wire, plus with the TS1’s floating AC/DC supply you’ll need to handle the signal ground for the RS-485.

The result of the logfile by telnet is :
IA INFO: mbtpc: m01 client connecting !
IA WARN: mbtcp(178) m1 bad message error

When I connect the Modbus TCP master directely to a Modbus TCP slave, I’m able to communicate so I don’t think that my master send bad messages…

In my master PLC, I send read/write requests. The PLC network diagnostic looks good.

Have you any idea ?