What I have observed is every time take out incoming power to any one of the VFDs, the rest of them get F72 comms error and fail to communicate with the PLC. Both setpoint and commands are sent through USS. In each V20 i use PZD word length of 2 and a PKW of 4. I then call the USS PORT SCAN 31 function in a cyclic OB set at 70ms cycle time. I then call this FC containing the FBs every 120ms from the MAIN OB. I use the USS DRIVE CONTROL 31 function block for each drive all located in a single FC and all using the same single instance DB as recommended by Siemens.
The drives are Simatic V20s daisychained to the bus and are properly terminated with resistors. Greetings everyone, I have a TIA V16 project in which I set up 7 drives to communicate with an S7 1500 controller via RS485 using USS protocol.