Let's Talk Modbus

[Steve Bailey]

Sorry moeen, I unzipped the archive to a project folder called "VersaMax", but I was unable to open it with VersaPro v 2.0

 

[RussB]

GE Fanuc COMM_REQ Wizard

This will help you to build your COMM_REQ logic. It is available through your GE Fanuc Application Engineer but is NOT supported by GE Fanuc technical support so please do not call them if you have problems with this. I would rather not get into trouble with them.
I can not get the file to attatch so I will put it in the DL area under "Other PLCs".

 

[moeen]

Well thanks Steve and everyone.......I have figured it out all..and I am working with Cimplicity Machine addition 5.5. I have the working program now. Among other things, the address format that the slave device expects is very important. Like some devices expect Holding registers to start from 3xxxx, but the modbus slave simulator software i was using intreprets address holding registers 2 to be holding register 1....strange..but its working........i have not talked to the actual EGCP units but i am sure that wouldn't be a big problem. I am attaching the program for anyone who might need it.

 

[BobB]

Watch the EGCP2 units. If I remember correctly, they list the words a being type 3 but they are really type 4 (read only). I think it is the usual confusion with Modbus/Jbus and addressing starting at either 0 or 1. The word type is pretty easy to change on line though. That is a blessing.

I know with Omron for some reason I often get words/bytes swapped. Just watch for that also. You really hjave to know what you are looking for in the way of a response. Say it is voltage, if the bytes/words are swapped, it is pretty easy to figure out. If it is varying current, then that is another story. Once you sort out one value you generally have no problems sorting out the others as they will be identical.

Some slave devices have a "big endian" "little endian" function. That is a huge help. I do not think the EGCP2 has that facility.

 

[moeen]

Well in reality i am using EGCP3 units. after i successfully configured modbus to work on rs232 port (the port 1 on versa max), i have now moved to rs485 port (15 pin port 2). and things are not going very smooth. as the logic has been tested to work on port 1 i suspect that i might have wrong connections. can anybody please help me with the pinouts from versa max 15 pin port 2 to port 1 on EGCP3 units.

thanks