Create a Modbus RTU network with AllenBradley PLC and Schneider VFD

[Puddle]

I had a similar problem with modbus a few days ago, seeing no data return and getting a time-out error. After going through all the possibilities, I think the thing I'd missed was the addressing. For holding registers you start at address 40001, so address 1 would be 40002.
Going on the assumption that in your code Cmd = 3 means that you're using function 3, this addressing shouldn't be required though. I was doing it with the modbus blocks in TIA portal, which gets the function code from a combination of mode and address, but if you can specify function then I wouldn't have thought the full address would be neccessary.

 

[thedolanduck]

Hello again, folks. I apologize for my delay in answering, I have been busy.


Long story short, I got it working using the SERIALISOL module, which we had to buy.


If you want the more detailed story: I contacted Rockwell Automation's support, the tech went through all the basic troubleshooting steps (even remoted to my laptop), but in the end didn't know what else to do, and ended up telling me that it was probably a faulty Mini DIN slot and I was to buy a SERIALISOL module. Which was, indeed, the case.


The tech also told me that the embedded serial port (Mini DIN slot) is not recommended for permanent communication, and was only intended for testing purposes as it is very fragile.


Draw your own conclusions. I know we probably claim this under warranty but we are way past our deadline and just want to finish this job. Thank you all for your help, you've been very kind to me.


Have a good week!