I am attempting to use a Digi one IA to convert RS 485 two wire to Modbus TCP. On the serial side of the Digi, I have an Eagle RTU that is set up as a master at 9600 8N1. On the LAN side of the Digi I have a industrial ethernet switch which is then connected to a Modicon PLC.
Any pointers…
Have you seen this application guide: http://ftp1.digi.com/support/documentation/90000638_a.pdf? Also, it depends on what the RTU is doing and what protocol it’s using. Is the RTU reading/writing to the PLC or is the PLC polling? If the PLC is polling then the RTU is slave, not master, and if it speaks straight ASCII then it also needs to be slave and you will use this application guide instead: http://ftp1.digi.com/support/documentation/90000648_a.pdf.
Your first hurdles will all be related to the RS-485 wiring, and perhaps grounding. Since the DOIA has a floating ground, you’ll want to somehow link the serial port ground pins of the DOIA to something the Eagle thinks is ground. If they only have 2 screws, finding that “something” could be hard.
You’ll want to setup the DOIA with a serial master and then add the destinations (routes) to the Modbus/TCP.
Then, use this info to confirm what you see from the eagle. If nothing shows, then you have no comms at all.
http://digitips.wikispaces.com/Digi_IA_Event_Trace