Reboot issue with Modbus RTU - PLC IDE

Official Hardware Pro Solutions Portenta Machine Control
1

I have set up a VFD to receive Modbus commands from the PLC.

There is a tutorial doc for setting up a new RS-485 channel and object, but that doesn't seem to be where the issue comes from.

Background program
Background program1000×538 23.6 KB

In short, I used a sysMbMRtu_FC06 function block as a Modbus function code 06 to write a single register corresponding to address 42331 (the VFD's speed input address).

This is run in a background program (MB_Task set as background program) as per the function block description.

When I download the code, it hangs up at 'Waiting for target to reboot'.

I can successfully escape the freeze by hitting the RST and then going back online.

I can open a simple program and download a ladder, no problem. The freezing is only when I add the Modbus function blocks (still stuck after about 10 mins, so something is definitely wrong with the reboot).

2

Can only do one image per post, so here is the RS-485 setup with the Modbus params.

RS485Setup
RS485Setup795×431 18.2 KB

3

And then finally, here is the function block used in the background program, along with its description.

FB_Desc

4

Here is my next path forward for using RS-485, but perhaps someone could verify if this is indeed the problem?

Does the RS-485 TX/RX share pins with the USB connection? In other words, as soon as I enable the RS-485, I immediately disable my USB connection to the computer?

I can't identify the exact pin designations from the pinout to determine if these use the same pins from the controller, but I have backed up a few steps, and the freezing occurs directly at the end of the download when I switch the RS-485 from 'disabled' to 'Modbus TCP'.

My next attempt will be programming the PMC over Ethernet.