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Communication between Modicon 984-145 and CEV 300 10
Trying to establish communication between Modicon 984-145 and CEV 300 10 modbus and Ethernet bridge

I'm trying to get a Modicon 984-145 talking to a CEV 300 10 modbus to ethernet bridge to no avail. I have verified the plc modbus port is working with a straight modbus cable to my pc. Serial settings on both the bridge and plc are rtu, 9600, 8, E, 1 and the serial port on the bridge is configured to a slave device. The modbus port is assigned 1 on the plc and in the advanced modbus protocol configuration of the bridge I have tried it as both fixed to 1 and as modbus/tcp header. We have the exact same setup at another location in the plant and the bridge and cable I made work just fine there. I also successfully used the bridge and cable on a 984-265 at my workstation. However when I try it on the system where I need to install it, all I get is the serial transmit light on the bridge flashing furiously and very slow modbus flashes(like 10 secs between flashes) on the plc. Any help is appreciated.

By Lynn August Linse on 4 March, 2013 - 10:23 am

One possible issue - the old 984 PLC need the correct linking of incoming DSR, or they won't talk. It just has to be high, not changing and not left floating.