Looking for pointers on getting RA's Modbus AOI to work.

[jstolaruk]

I'm trying to get a 5069-L306er to talk to a Automation Direct ProSence Controller by using RA's AOI for modbus client but its stuck not getting a message back. Hoping one of the experts here can steer me to what I'm doing wrong.

I've got the Prosense setup with a valid IP address, the AOI reports it has created a socket instance and sets the Sts_Connected output ON. Monitoring the AOI's logic, it creates a new instance (Wrk_Instance) every time I cycle the enable bit.

The AOI indicates it successfully sends a read message (Ref_MsgRead) by setting the message done bit and not the error bit. I placed counters on the enable, done, and error bits to track.

But the Sts_Overload and Sts_Overlap bits cycle ON when just enabling a single read transaction and the destination elements are empty.

I've tested the connection to the ProSence with a number of PC Modbus tools, Modbus_Poll and ModScan64, and they both successfully can send a simple holding register read request, and both agree on the data coming back.

Any thoughts about what I can try next? should I emulating the Prosense on the PC by using ModSim64?

Last resort is to get some h/w but I only need to monitor/modify a single setpoint at very long intervals.

Thanks in advance!

 

[JeremyM]

What is the station ID, did you set such in the client parameters?

The target device is indeed natively Modbus/TCP?

I re-wrote the whole thing to accept a variable number of transactions, a single AOI, and a lot less memory, so I’m fairly familiar on this one.

 

[jstolaruk]

At first I set it zero as the RA document suggested. Try something other than zero?

 

[JeremyM]

Most Modbus servers default to 1.

 

[jstolaruk]

Sir, you get a huge atta-boy, thank you!

 

[JeremyM]

Did it work?

 

[jstolaruk]

Yes, I owe you a beer!

 

[JeremyM]

Sweet, I’ll drink another beer since this isn’t one of those cliffhanger-because-the-OP-disappears threads.

 

[Contr_Conn]

Modbus TCP is such a loose standard, so nobody follows it anymore.
AOI follows the standard that requires to have StationID (or UID) =0 unless you have a multiple devices (or stations) within the same IP address. Good example is a bank of valves where each valve will have own StationID starting at 1, while adapter keeps StationID=0.
Another example is I/O rack, with adapter using StationID=0, then modules 1, 2, etc.
From my experience, if you have “Connected” but transactions are failing then try StationID=1 or 255. This usually works.

 

[jstolaruk]

From my experience, if you have “Connected” but transactions are failing then try StationID=1 or 255. This usually works.

As it turned out, that was exactly what fixed my dilemma, thank you JeremyM for shaking that loose so quickly. I had followed the recommendation in the RA document that said set it zero.

The last time I recall doing anything with Modbus was in the mid-80s when I had to write a driver to access data out of a Modicon 584. But other than remembering I had done something, the details were long gone.

Thanks for everyone's help!