RSLogix 5000 Ladder Diagram for Modbus


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I am using a ControLogix PLC with the ProSoft MVI69-MNET ModbusTCP interface to communicate with a 3rd party master.

I am able to map the information from the ladder diagram using the MOV function and the 3rd party master reads the information properly.

However when I write using the master over to the ProSoft I can see the values on the MNET.DATA.ReadData[X] section but I cannot transfer that information to my ladder diagram tags.

Any ideas?


For starters, it looks to me that you are either using one of the following combinations as the two devices you quoted are not advertised as compatible on the Prosoft website:

- Compact Logix PLC with a MVI69-MNET card
- Control Logix PLC with a MVI56E-MNETC card.

I will assume that you are using a CompactLogix PLC as you quoted MNET.XXX as your tag. There are two sets of tag matrices that are set up for data transfer, one is the "MNET.DATA.ReadData[X]" matrix which is used to transfer the data from the field device to the PLC via the commands set up in the MVI card.

The other is the "MNET.DATA.WriteData[X]" matrix which is used to transfer the data from the PLC to the field device via the commands set up in the MVI card if the PLC is the master.

As you have mentioned above, the PLC you are using is a slave, so you just need to write the required data to the appropriate section in the required tag in the "MNET.DATA.WriteData[X]" matrix. There should be no need to set up any commands in the MVI card as I think that the MVI card will automatically look at the matrix and store it in it's memory.

If you are using a Control Logix PLC, then the process is very much the same, just a slight variance in both of the tag matrix names.

Hope that helps...