Newbie networking problem with DSC Module and Modbus over Ethernet

[MartinMcD]

Hello there,

I'm using the DSC module for the first time to communicate with a PLC using Modbus Ethernet, or rather I'm trying to.

During initial commisioning what I found was that the PLC could not see the Modbus Client that the DSC module was running.  I took a step back and confirmed:

- Using 2 laptops connected to the work network (wired and WiFi) I could have the DSC module running on one PC and read the shared variables on another using LabVIEW

- To take a step closer to reality I then used the ModScan application on the 'PLC-stand-in' laptop to see if I could connect to the DSC Modbus client without using LabVIEW, which I could

- I then disconnected both laptops from the work network and connected them directly together using a network cable and assigned IP addresses. I didn't need a crossover cable because of Auto-MDIX. The PCs could ping each other but the 'PLC-stand-in' laptop running ModScan could no longer connect to the DSC Modbus laptop. I'm confident if I can get this step to work the actual setup will work.

I don't understand networking well enough to know what the problem is, perhaps it is something obvious to a non-newbie.  I'm aware my laptops are logged on to a windows domain so I wondered if that was why a direct connection wouldn't work.  I don't know if I need to create a network rather than just physically connect the 2 devices together. Or whether IT would have to add the PLC to the company domain, which I'm not sure they'd be happy to do if it is even possible. 

Any tips would be most welcome and appreciated,

Thank you,

Martin

[unclebump]

Shows us the ip config info for the plc ethernet port and the computer lan port. We need the ip address, gateway, and subnet mask info. You definitely don't want this connected to the corporate network, it will interfere with the update speed. Can you have these devices directly connected, or are they too far apart? If you don't have the NI OPC server product, download a demo of Kepware OPC server and use the opc client to test network connection to plc. You can also use wireshark to see what is happening on the computer ethernet port.