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!