I have had hit and miss success hooking up trunks consisiting of one to six Allen-Bradley Powerflex 400 VFD's to FLN trunks in our Siemens control panels. Sometimes I hook them up and configure the drives and they just consistently talk perfectly without failure. Other times I can't get them to talk at all using all the same settings.

What's really confusing me now, is that I can get the whole trunk to talk for maybe an hour or two and then lose communication to them all after that. They don't automatically re-connect and I have to go through and cycle power to the 5 that are currently on the trunk and then they will talk for a while again before losing communication.

I am using application #2735 on a Siemens PXCM modular controller, wiring for the trunk is all daisy-chained 18ga. shielded. The drives are configured for 9600, P1 8-N-1, and I've checked for conflicting duplicate node addresses. What else can a check to ensure consistent communications?