Gary, I'd be happy to help you on this but you might want to explain a bit further just what you want to do.
I'm not clear on a couple of things: First, for the PLC to control the VFD you have to wire SOMETHING! Either you wire discreet PLC outputs directly to the VFD inputs to control things like START/STOP, FORWARD/REVERSE, etc. or, second, you wire a fieldbus cable (usually RS-485) and do all your control over the fieldbus.
You may also want to take some drive outputs back to your PLC inputs. DRIVE FAULTED, RUN VERIFICATION, ANALOG SPEED OR TORQUE signals, etc. Again, these can be done with discreet wiring or thru the fieldbus.
Fill us in a little more completely and we'll try to help you.