Connection between bridge and a PLC


Thread Starter

David M

Hi, i'm trying to make a connection between a 174 CEV 300 10 (Modbus to Ethernet Bridge), we try the conection to a 984 PLC, and it was possible, but when i try to use the same bridge to conect with a 140CPU113, the connection wasnt possible, why? i dont know, i read the bridge's manual and the indicated PLC doesnt appear in the list of devices, so i need to know why the connection wasnt possible, i use 3 bridges to make the connections and i always got the same error... could you help me with this?
There should be no difference other than perhaps the Modbus address of the 2 PLCs. The bridge doesn't care what device it's attached to, and the same configuration should work for either PLC.

When you try to talk through the bridge, you have to include a map index. That map index should be the MB address of the device you want to speak to. For example, in my classroom, I have one of these bridges. IP address is, and it's connected on the MB side to a Compact PLC, whose MB address is 7. So in Concept or Proworx, when I want to get online with the PLC, I go via ethernet gateway to index 7, and it's online.


Humberto Nunes

I've used the exact same device to communicate to a Momentum PLC. It also worked with a Quantum, but the pinouts for Modbus communications were different. This may be one problem. Also, check the Modbus communications setup on the Quantum, it may be set up for a different baud rate, or it may be in ASCII instead of RTU.

Good Luck
Humberto Nunes
If you are using concept V2.2, configuration of Ethernet card has to select the default Frame type Ethernet II for your Quantum Ethernet Card. We faced the typical problem of the Modicon Bridge and we used to put IEC 802.3 as the Frame
and broke our heads over this problem. Check for configuration of the Bridge and IP address if the problem still exists in Frame II?
The most likely problem is "cable problems". I'm not familiar with the 140CPU, but you'll need to loop back the DTR/DSR and RTS/CTS on the PLC. All Modicon software/PLC seem to have this need - older products especially.

The CEV doesn't care about DTR/DSR nor RTS/CTS (unless you enable the RTS/CTS for radio modem support). Also, the CEV is only dimly "Modbus
aware" - it doesn't try to enforce any specific list of commands and supports Enron Modbus and other variations.

Best Regards

Lynn August Linse, Senior IA Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected]
Tel: (949)300-6337 Fax: (949)453-7152