EN2MB-R - Function 06 Not Always Writing


I have setup a test bench using the EN2MB-R gateway tansmitting Modbus TCP data between a 1756-L81E processor and a Modbus Server configured by a third-party vendor. I have no access to modify the configuration of the modbus server, but I have the addressing provided.

There are 2 function codes available for this modbus server - 03 and 06. Function code 03 is working fine, and I am correctly reading the information from the server in real-time. Function code 06 does not always work. At times the registers are written; other times it could take up to 30 minutes for the register to be written. The timing of the register write is very inconsistent.

Using the transaction monitor in the configuration manager, the value is matching correctly to the value I am writing from the PLC.

I’ve tried pulling exception codes from the device using a MSG instruction, but thus far have received nothing.

I have attached the mapping from the vendor, as well as my communication below.

Thanks in advance!



What is ther response of the of the write transaction?

I know you said you only have the mapping, but is there a way you to see the value update on the modbus end?

If the gateway is consistently sending and recieving replies, then the gateway is functioning as it should. Are you able to check the settings on the Modbus device?

Hi Kevin,

Thank you for the quick response -

Unfortunately I can’t see the individual command responses; I only have a tool from N-Tron which gives me text-based information (PCG SDK Manager).

I will contact the vendor as well regarding the situation.


If you use the Node monitor in the EN2MB-R, do you see any exceptions codes that occur?

Hi Kevin,

By node monitor do you mean the transaction monitor in the configuration manager? I only have seen how to pull the exception codes via a MSG instruction.

Yes. I would use the monitor to capture any exception codes that could be occuring on the device.