What exactly are you doing here? I think you mean you have a comm handle configured to open to 127.0.0.1:8502, yes? So the PAC Sim is reading data from the simulator and everything is running on the localhost, so all is good.
Okay, so this is listening on the local computer on port 8502 - The 127.x.x.x IP range is only localhost, which PAC Sim would be able to “see” since it also is running on the local computer. The EPIC PR1 will not be able to communicate to any simulator running on localhost on your computer.
Again, not sure what you are doing here. Are you are running the same strategy that you were running on PAC SIM on the EPIC PR1? What do you have the comm handle in your strategy set to? If it is still 127.0.0.25:8502, then you are talking to the PR1 itself (You could be using 127.0.0.1:8502 as it is the same thing). Since the PR1 has a modbus server, you got a response, and it told you the address you requested is invalid.
Since you are getting a 2-Invalid address response, you are requesting a register that doesn’t exist on the PR1, as you have discovered. Use the Modbus calculator that @Beno posted about to look up the “Register Address” and add 1 to it to get the Modbus register. You will also need to change the slave address parameter to the Unit ID # that was given in the calculator.
Note for Opto22: The calculator should be captioned either “Address” or “Register” and not both, as these mean subtly different things in Modbus. The Modbus Address is the Modbus Register minus 1. I know every other manufacturer does the same thing… sigh.