Modbus TCP/IP on Beckhoff CX9000

[Gedasss]

Hi,
I have a problem with implementation of Modbus TCP/IP on CX9000.
I did install Tc.ModbusSrv.lib in Twincat ( i use Twincat 2.10 v).
I'd like to know how make communication between HMI ( like a pc, using modbus slave program ) and CX9000 via Modbus TCP/IP protocol.
Can anybody help in step-by-step explanation or program example?

 

[akira]

Hello Gedasss,
Did you know to make that communication? I am in the same situation right now
Or... somebody knows how to do that?

Thanks in advance.

 

[LadderLogic]

Well, it is an old thread, but...

A long time ago I was palying with Modbus communications to a BC9120 controller. After spending a lot of time trying to make any sense out of Beckhoff's Help file and some trial and error, I found that:

1. As Modbus has no idea about TwinCAT variable names, any variable that needs to be accessible via Modbus, should be declared with a specific address: %MW00000, %MW00002 and so on.

2. The Beckhoff controller internal memory (also called 'markers', also a I hate this word for being confusing) begins at offset 4000 hex in the image. Modbus internal memory ('holding registers') addresses start at 400001 and up. Therefore, in order to access controller address %MW0000, the Modbus client should call adress 416385 (4000 hex = 16384 dec; 16384 + 400001 = 416385)

3. Note that Beckhoff internal addresses are numbered by bytes, while Modbus addresses are in words. So Modbus address 416386 would point to %MW0002, not %MW0001; 416387 point to %MW0004 and so on. I just put both Beckhoff and Modbus addresses next to each other in an Excel file so it would be easy to find the match.

Good luck. I remember it worked also now, so much later, I would not vouch for it.