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. The drives are Simatic V20s daisychained to the bus and are properly terminated with resistors. 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. I then call this FC containing the FBs every 120ms from the MAIN OB. I then call the USS PORT SCAN 31 function in a cyclic OB set at 70ms cycle time. In each V20 i use PZD word length of 2 and a PKW of 4. Both setpoint and commands are sent through USS. 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. Is this behaviour normal? What causes it? I use an RS485/ 422 PtP BA module sending data at 19200bps. Strangely enough it doesn't show any fault even though the diagnostics interupt setting is enabled on it. What I noticed is that as I was setting up the VFDs one by one, the F72 fault on the BOPs only pop up on an already configured drives. So, the VFDs that hadn't been commissioned yet for RS485, but were already physicaly terminated/ connected to the PLC, didn't fault the bus when they were powered down. They only faulted the bus upon switching them off only after RS485 activation (post commissioning).
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