Communication Issue, Banner DX80 & Rockwell Micro 820 PLC


Thread Starter

Charles Casalie

I am attempting to establish Modbus communications between a Banner DX80 Sure Cross Performance Gateway and a Rockwell Micro 820 PLC using the PLC's built-in RS-485 port.

I have been working with both Banner & Rockwell tech support and have come to an impasse.

I have the PLC as Master and the DX80 as Slave (the Banner cannot be a Modbus Master).

When I trigger a Modbus Read from the PLC, the #2 light on the DX 80 flashes Red indicating it received some traffic, but was unable to understand it. The Modbus command on the PLC gives and error code of 55 which Rockwell tells me is a timeout due to no response from the slave.

I have checked all comm parameters on both devices and everything seems correct.

Rockwell tells me that I don't need termination or biasing resistors on the RS-485 lines.

Anyone with any experience with this particular configuration or with Modbus Communications on the Micro 800 series have any suggestions?
Sorry, no A-B experience.

1) If the master times out, it means the Banner did not reply.

If you addressed the wrong slave node, then the Banner would ignore the message. Are you sure you're addressing the correct NID (network ID) value in the gateway? The left rotary switch sets up the NID value.

2) I'm not sure what the Banner response is if your register address is invalid. Are you sure you're hitting a valid register address?

3) are you sure you're using the 03 reading holding registers function code?

4) The Banner configuration cable is a USB/RS-485 converter. Can you talk to the gateway with a generic Modbus master like Simply Modbus, Modscan32 or the ICPDAS master via the Banner cable?